Home Books Review of Medical Microbiology & Immunology: A Guide to Clinical Infectious Diseases, 15e

Previous Chapter

Next Chapter

Review of Medical Microbiology & Immunology: A Guide to Clinical Infectious Diseases, 15e

Part II: Clinical Bacteriology

Listen

The main reason why some bacteria are anaerobes (i.e., they cannot grow in the presence of oxygen) is because:

(A) they do not have sufficient catalase and superoxide dismutase.

(B) they have too much ferrous ion that is oxidized to ferric ion in the presence of oxygen.

(C) they have unusual mitochondria that cannot function in the presence of oxygen.

(D) transcription of the gene for the pilus protein is repressed in the presence of oxygen.

Which one of the following sets consists of bacteria that are both anaerobes?

(A) Actinomyces israelii and Serratia marcescens

(B) Campylobacter jejuni and Vibrio cholerae

(C) Clostridium perfringens and Bacteroides fragilis

(D) Mycobacterium tuberculosis and Pseudomonas aeruginosa

(E) Mycoplasma pneumoniae and Corynebacterium diphtheriae

You’re in the clinical laboratory looking at a Gram stain when the laboratory technician comes up to you and says, “I think your patient has Staph epi [short for Staphylococcus epidermidis] bacteremia.” Which one of the following sets of results did the tech find with the organism recovered from the blood culture?

(A) Gram-positive cocci in chains, catalase-positive, coagulase-positive

(B) Gram-positive cocci in chains, catalase-negative, coagulase-negative

(C) Gram-positive cocci in clusters, catalase-positive, coagulase-negative

(D) Gram-positive cocci in clusters, catalase-negative, coagulase-positive

(E) Gram-positive diplococci, catalase-negative, coagulase-positive

Superantigen production by Staphylococcus aureus is involved in the pathogenesis of which one of the following diseases?

(A) Impetigo

(B) Osteomyelitis

(C) Scalded skin syndrome

(D) Septicemia

(E) Toxic shock syndrome

Which one of the following is the virulence factor produced by Staphylococcus aureus that prevents the activation of complement and thereby reduces opsonization by C3b?

(A) Catalase

(B) Coagulase

(C) Endotoxin

(D) Protein A

(E) Teichoic acid

The main reason why methicillin-resistant Staphylococcus aureus (MRSA) strains are resistant to methicillin and nafcillin is:

(A) they produce β-lactamase that degrades the antibiotics.

(B) they have altered penicillin-binding proteins that have reduced binding of the antibiotics.

(C) they have mutant porin proteins that prevent the antibiotics from entering the bacteria.

(D) they have plasmid-encoded export proteins that remove the drug from the bacteria.

A pore-forming exotoxin produced by Staphylococcus aureus that kills cells and is important in the severe, rapidly spreading necrotizing lesions caused by MRSA strains is:

(A) coagulase.

(B) enterotoxin.

(C) exfoliatin.

(D) P-V leukocidin.

(E) staphyloxanthin.

Of the following antibiotics, which one is the most appropriate to treat a severe necrotizing skin infection caused by an MRSA strain of Staphylococcus aureus?

(A) Amoxicillin

(B) Ceftriaxone

(C) Ciprofloxacin

(D) Gentamicin

(E) Vancomycin

An outbreak of serious pneumococcal pneumonia and sepsis among inmates in an overcrowded prison has occurred. Laboratory analysis determined that one serotype was involved. The prison physician said that the pneumococcal vaccine might have limited the outbreak. Which one of the following structures of the pneumococcus is responsible for determining the serotype and is also the immunogen in the vaccine?

(A) Capsule

(B) Flagellar protein

(C) O antigen

(D) Peptidoglycan

(E) Pilus protein

Which one of the following best describes the pathogenesis of rheumatic fever?

(A) An exotoxin produced by Streptococcus pyogenes that acts as a superantigen damages cardiac muscle.

(B) An exotoxin produced by Streptococcus pyogenes that ADP-ribosylates a G protein damages joint tissue.

(C) Antibody to the capsular polysaccharide of Streptococcus pyogenes cross-reacts with joint tissue and damages it.

(D) Antibody to the M protein of Streptococcus pyogenes cross-reacts with cardiac muscle and damages it.

(E) Endotoxin produced by Streptococcus pyogenes activates macrophages to release cytokines that damage cardiac muscle.

Which one of following laboratory tests is the most appropriate to distinguish Streptococcus pyogenes from other β-hemolytic streptococci?

(A) Ability to grow in 6.5% NaCl

(B) Activation of C-reactive protein

(C) Hydrolysis of esculin in the presence of bile

(D) Inhibition by bacitracin

(E) Inhibition by optochin

Infections by which one of the following bacteria are typically treated with penicillins such as amoxicillin, because they exhibit neither low-level resistance nor high-level resistance and synergy with an aminoglycoside is not required in order for penicillins to be effective?

(A) Enterococcus faecalis

(B) Staphylococcus aureus

(C) Staphylococcus epidermidis

(D) Streptococcus pneumoniae

(E) Streptococcus pyogenes

Your patient in the emergency room has a 5-cm ulcer on her leg that is surrounded by a red, warm, and tender area of inflammation. You do a Gram stain on pus from the ulcer and see gram-positive cocci in chains. Culture of the pus grows small β-hemolytic colonies that are catalase-negative and are inhibited by bacitracin. These results indicate that the organism causing her lesion is most likely:

(A) Enterococcus faecalis.

(B) Staphylococcus aureus.

(C) Streptococcus agalactiae.

(D) Streptococcus pneumoniae.

(E) Streptococcus pyogenes.

The Jones family of four had a delicious picnic lunch last Sunday. It was a warm day, and the food sat in the sun for several hours. Alas, 3 hours later, everyone came down with vomiting and nonbloody diarrhea. In the emergency room, it was found that Mrs. Jones, who prepared the food, had a paronychia on her thumb. Which one of the following is the most likely causative organism?

(A) Enterococcus faecalis

(B) Staphylococcus aureus

(C) Staphylococcus epidermidis

(D) Streptococcus agalactiae

(E) Streptococcus pyogenes

A 20-year-old sexually active woman reports dysuria and other symptoms of a urinary tract infection. Gram stain of the urine reveals gram-positive cocci. Which one of the following sets of bacteria is most likely to cause this infection?

(A) Staphylococcus aureus and Streptococcus pyogenes

(B) Staphylococcus saprophyticus and Enterococcus faecalis

(C) Streptococcus agalactiae and Staphylococcus epidermidis

(D) Streptococcus pneumoniae and Enterococcus faecalis

(E) Streptococcus pyogenes and Streptococcus pneumoniae

Your patient is a 2-week-old infant who was well until 2 days ago, when she stopped feeding and became irritable. She now has a fever to 38°C, has developed a petechial rash all over her body, and is very difficult to arouse. In the emergency room, a blood culture and a spinal tap were done. Gram stain of the spinal fluid showed gram-positive cocci in chains. Culture of the spinal fluid on blood agar revealed β-hemolytic colonies that grew in the presence of bacitracin and hydrolyzed hippurate. Which one of the following is the most likely causative organism?

(A) Staphylococcus aureus

(B) Streptococcus agalactiae

(C) Streptococcus mutans

(D) Streptococcus pneumoniae

(E) Streptococcus pyogenes

Your patient is a 50-year-old woman who has a community-acquired pneumonia caused by Streptococcus pneumoniae. Antibiotic susceptibility tests reveal an MIC of less than 0.1 mg/mL to penicillin G. Which one of the following is the best antibiotic to treat the infection?

(A) Clindamycin

(B) Gentamicin

(C) Metronidazole or doxycycline

(D) Penicillin G or levofloxacin

(E) Vancomycin

Your patient is a 70-year-old man with endocarditis caused by Enterococcus faecalis. Which one of the following is the best combination of antibiotics to treat the infection?

(A) Azithromycin and trimethoprim-sulfamethoxazole

(B) Chloramphenicol and rifampin

(C) Doxycycline and levofloxacin

(D) Metronidazole and clindamycin

(E) Penicillin G and gentamicin

Regarding the differences between N. meningitidis (meningococci) and N. gonorrhoeae (gonococci), which one of the following is the most accurate statement?

(A) Meningococci are oxidase-positive, whereas gonococci are not.

(B) Meningococci have a thick polysaccharide capsule, whereas gonococci do not.

(C) Meningococci have lipid A, whereas gonococci do not.

(D) Meningococci produce penicillinase, whereas gonococci do not.

(E) Meningococci synthesize IgA protease, whereas gonococci do not.

Your patient is a 14-year-old girl who was sent home from school because she had a fever of 102°C and a severe headache and was falling asleep in class. When her fever rose to 104°C, her mother took her to the emergency room, where a blood pressure of 60/20 mm Hg and several petechial hemorrhages were found. Gram-negative diplococci were seen in a Gram stain of the spinal fluid. Which one of the following is most likely to cause the fever, hypotension, and petechial hemorrhages?

(A) Endotoxin

(B) IgA protease

(C) Oxidase

(D) Pilus protein

(E) Superantigen

(A) Azithromycin

(B) Doxycycline

(C) Penicillin G

(D) Rifampin

(E) Trimethoprim-sulfamethoxazole

Regarding the differences between N. meningitidis (meningococci) and N. gonorrhoeae (gonococci), which one of the following is the most accurate statement?

(A) Humans are the reservoir for both organisms.

(B) Many clinical isolates of meningococci produce β-lactamase, but clinical isolates of gonococci do not.

(C) Meningococci have multiple antigenic types, but gonococci have only one antigenic type.

(D) The conjugate vaccine against gonorrhea contains seven types of the pilus protein as the immunogen.

(E) The main mode of transmission for both organisms is respiratory droplets.

Your patient is a 20-year-old man with a urethral exudate. You do a Gram stain of the pus and see gram-negative diplococci with neutrophils. Which one of the following is the best antibiotic to treat the infection?

(A) Ceftriaxone

(B) Gentamicin

(C) Penicillin G

(D) Trimethoprim-sulfamethoxazole

(E) Vancomycin

Which one of the following is a club-shaped, gram-positive rod that causes disease by producing an exotoxin that kills cells by inhibiting elongation factor-2, resulting in the inhibition of protein synthesis?

(A) Bacillus anthracis

(B) Bacillus cereus

(C) Clostridium perfringens

(D) Corynebacterium diphtheriae

(E) Listeria monocytogenes

Which one of the following is a large gram-positive rod that causes necrosis of tissue by producing an exotoxin that degrades lecithin, resulting in the lysis of cell membranes?

(A) Bacillus anthracis

(B) Bacillus cereus

(C) Clostridium perfringens

(D) Corynebacterium diphtheriae

(E) Listeria monocytogenes

Which one of the following sets of bacteria causes disease characterized by a pseudomembrane?

(A) Bacillus anthracis and Listeria monocytogenes

(B) Bacillus cereus and Clostridium perfringens

(C) Bacillus cereus and Clostridium tetani

(D) Corynebacterium diphtheriae and Clostridium difficile

(E) Corynebacterium diphtheriae and Listeria monocytogenes

Disease caused by which one of the following sets of bacteria can be prevented by a toxoid vaccine?

(A) Bacillus anthracis and Clostridium botulinum

(B) Bacillus anthracis and Clostridium perfringens

(C) Bacillus cereus and Clostridium tetani

(D) Corynebacterium diphtheriae and Clostridium tetani

(E) Corynebacterium diphtheriae and Listeria monocytogenes

Your patient in the pediatric intensive care unit is a 2-week-old boy with a high fever and the signs of meningitis. Gram stain of the spinal fluid reveals small gram-positive rods. Colonies on blood agar show a narrow zone of β-hemolysis. Which one of the following is the most likely cause of his neonatal meningitis?

(A) Bacillus anthracis

(B) Bacillus cereus

(C) Clostridium perfringens

(D) Corynebacterium diphtheriae

(E) Listeria monocytogenes

(A) Doxycycline

(B) Gentamicin

(C) Metronidazole

(D) Trimethoprim-sulfamethoxazole

(E) Vancomycin

Your patient is a 40-year-old woman with diplopia and other signs of cranial nerve weakness. History reveals she grows her own vegetables and likes to preserve them in jars that she prepares at home. She is fond of her preserved string beans, which is what she ate uncooked in a salad for dinner last night. Which one of the following is the most likely cause of this clinical picture?

(A) Bacillus anthracis

(B) Clostridium botulinum

(C) Clostridium perfringens

(D) Clostridium tetani

(E) Listeria monocytogenes

Your patient is a 30-year-old man with a 2-cm lesion on his arm. It began as a painless papule that enlarged and, within a few days, ulcerated and formed a black crust (eschar). He works in an abattoir where his job is removing the hide from the cattle. A Gram stain of fluid from the lesion reveals large gram-positive rods. Which one of the following bacteria is likely to be the cause?

(A) Bacillus anthracis

(B) Clostridium botulinum

(C) Clostridium perfringens

(D) Clostridium tetani

(E) Listeria monocytogenes

Your patient is a 30-year-old man who was brought to the emergency room following a motorcycle accident in which he sustained a compound fracture of his leg. He now has a high fever and a rapidly spreading cellulitis with crepitus in the area of the fracture. Large gram-positive rods are seen on the exudate. Necrotic tissue was debrided. Which one of the following is the best antibiotic to treat the infection?

(A) Azithromycin

(B) Ciprofloxacin

(C) Gentamicin

(D) Penicillin G

(E) Vancomycin

Your patient is a 65-year-old woman who is several days post-op following removal of her carcinoma of the colon. She now spikes a fever and has a cough, and chest X-ray shows pneumonia. While being treated with the appropriate antibiotics, she develops severe diarrhea. You suspect she may have pseudomembranous colitis. Which one of the following is the best antibiotic to treat the infection?

(A) Ceftriaxone

(B) Doxycycline

(C) Gentamicin

(D) Metronidazole

(E) Trimethoprim-sulfamethoxazole

Your patient is a 75-year-old man with an indwelling urinary catheter following prostatectomy for prostate cancer. He now has the sudden onset of fever to 40°C, blood pressure of 70/40 mm Hg, and a pulse of 140 bpm. You draw several blood cultures, and the laboratory reports that all are positive for a gram-negative rod that forms red pigmented colonies. Which one of the following bacteria is the most likely cause of this infection?

(A) Escherichia coli

(B) Klebsiella pneumoniae

(C) Proteus mirabilis

(D) Pseudomonas aeruginosa

(E) Serratia marcescens

You’re a public health epidemiologist who is called to investigate an outbreak of bloody diarrhea in 16 people. You find that it is associated with eating rare hamburgers in a particular fast-food restaurant. A culture of the remaining uncooked hamburger grows a gram-negative rod that produces a dark purple colony on EMB agar, which is evidence that it ferments lactose. Which one of the following bacteria is the most likely cause of this outbreak?

(A) Escherichia coli

(B) Salmonella enterica

(C) Salmonella typhi

(D) Shigella dysenteriae

(E) Vibrio cholerae

Your patient has third-degree burns over most of his body. He was doing well until 2 days ago, when he spiked a fever, and his dressings revealed pus that had a blue-green color. Gram stain of the pus revealed a gram-negative rod that formed colorless colonies on EMB agar. Which one of the following bacteria is the most likely cause of this infection?

(A) Campylobacter jejuni

(B) Escherichia coli

(C) Haemophilus influenzae

(D) Pseudomonas aeruginosa

(E) Salmonella enterica

Your patient has third-degree burns over most of his body. He was doing well until 2 days ago, when he spiked a fever, and his dressings revealed pus that had a blue-green color. Gram stain of the pus revealed a gram-negative rod that formed colorless colonies on EMB agar, which one of the following is the best combination of antibiotics to treat the infection?

(A) Azithromycin plus gentamicin

(B) Doxycycline plus gentamicin

(C) Metronidazole plus gentamicin

(D) Piperacillin/tazobactam plus gentamicin

(E) Vancomycin plus gentamicin

Regarding the members of the family Enterobacteriaceae, which one of the following statements is the most accurate?

(A) All members of the family are anaerobic, which means they must be cultured in the absence of oxygen.

(B) All members of the family ferment lactose, which is an important diagnostic criterion in the clinical laboratory.

(C) All members of the family have endotoxin, an important pathogenetic factor.

(D) All members of the family produce an enterotoxin, which ADP-ribosylates a G protein in human enterocytes.

You’re on a summer program working in a clinic in a small village in Ecuador. There is an outbreak of cholera, and your patient has massive diarrhea and a blood pressure of 70/40 mm Hg. Which one of the following would be the most appropriate action to take?

(A) Administer antimotility drugs to diminish the diarrhea.

(B) Administer intravenous saline to replenish volume.

(C) Administer tetracycline to kill the organism.

(D) Perform stool cultures and fecal leukocyte tests to make an accurate diagnosis.

Your patient is a 20-year-old woman with diarrhea. She has just returned to the United States from a 3-week trip to Peru, where she ate some raw shellfish at the farewell party. She now has severe watery diarrhea, perhaps 20 bowel movements a day, and is feeling quite weak and dizzy. Her stool is guaiac-negative, a test that determines whether there is blood in the stool. A Gram stain of the stool reveals curved gram-negative rods. Culture of the stool on MacConkey’s agar shows colorless colonies. Which one of the following bacteria is the most likely cause of this infection?

(A) Escherichia coli

(B) Helicobacter pylori

(C) Proteus mirabilis

(D) Pseudomonas aeruginosa

(E) Vibrio cholerae

Your patient is a 6-year-old boy with bloody diarrhea for the past 2 days accompanied by fever to 40°C and vomiting. He has a pet corn snake. Blood culture and stool culture from the boy and stool culture from the snake (taken very carefully!) revealed the same organism. The cultures grew a gram-negative rod that formed colorless colonies on EMB agar. Which one of the following bacteria is the most likely cause of this infection?

(A) Helicobacter pylori

(B) Proteus mirabilis

(C) Salmonella enterica

(D) Shigella dysenteriae

(E) Vibrio cholerae

Your patient is a 25-year-old woman with pain on urination and cloudy urine but no fever or flank pain. She has not been hospitalized. You think she probably has cystitis, an infection of the urinary bladder. A Gram stain of the urine reveals gram-negative rods. Culture of the urine on EMB agar shows colorless colonies, and a urease test was positive. Swarming motility was noted on the blood agar plate. Which one of the following bacteria is the most likely cause of this infection?

(A) Escherichia coli

(B) Helicobacter pylori

(C) Proteus mirabilis

(D) Pseudomonas aeruginosa

(E) Serratia marcescens

Your patient has abdominal pain, and a mass is discovered in the left lower quadrant. Upon laparotomy (surgical opening of the abdomen), an abscess is found. Culture of the pus reveals Bacteroides fragilis. Regarding this organism, which one of the following is the most accurate?

(A) A stage in the life cycle of Bacteroides fragilis involves forming spores in the soil.

(B) Bacteroides fragilis is an anaerobic gram-negative rod whose natural habitat is the human colon.

(C) Bacteroides fragilis produces black colonies when grown on blood agar.

(D) Pathogenesis by Bacteroides fragilis involves an exotoxin that increases cyclic AMP by ADP-ribosylation of a G protein.

(E) The toxoid vaccine should be administered to prevent disease caused by Bacteroides fragilis.

Your patient has abdominal pain, and a mass is discovered in the left lower quadrant. Upon laparotomy (surgical opening of the abdomen), an abscess is found. Culture of the pus reveals Bacteroides fragilis. Which one of the following is the best antibiotic to treat the infection?

(A) Doxycycline

(B) Gentamicin

(C) Metronidazole

(D) Penicillin G

(E) Rifampin

Your patient in the gastrointestinal clinic is a 50-year-old insurance salesman with what he describes as a “sour stomach” for several months. Antacids relieve the symptoms. After taking a complete history and doing a physical examination, you discuss the case with your resident, who suggests doing a urea breath test, which tests for the presence of urease. Which one of the following bacteria does the resident think is the most likely cause of the patient’s disease?

(A) Helicobacter pylori

(B) Proteus mirabilis

(C) Salmonella enterica

(D) Serratia marcescens

(E) Shigella dysenteriae

Your patient is a 35-year-old woman with epilepsy who had a grand-mal seizure about 2 months ago. She comes to see you now because she has been coughing up foul-smelling sputum for the past week. Chest X-ray reveals a cavity with an air-fluid level. Gram stain of the sputum reveals gram-negative rods, and culture reveals black colonies that grow on blood agar only in the absence of air. Which one of the following bacteria is the most likely cause of this infection?

(A) Bacteroides fragilis

(B) Campylobacter jejuni

(C) Klebsiella pneumoniae

(D) Prevotella melaninogenica

(E) Proteus mirabilis

Your patient is a 75-year-old man who has smoked cigarettes (two packs a day for more than 50 years) and consumed alcoholic drinks (a six pack of beer each day) for most of his adult life. He now has the signs and symptoms of pneumonia. Gram stain of the sputum reveals neutrophils but no bacteria. Colonies appear on buffered charcoal yeast (BYCE) agar but not on blood agar. Which one of the following bacteria is most likely to be the cause of his pneumonia?

(A) Bordetella pertussis

(B) Haemophilus influenzae

(C) Klebsiella pneumoniae

(D) Legionella pneumophila

(E) Pseudomonas aeruginosa

(A) Azithromycin

(B) Ceftriaxone

(C) Gentamicin

(D) Metronidazole

(E) Piperacillin/tazobactam

Your patient is a 6-year-old boy who is complaining that his ear hurts. His mother says this began yesterday and that he has a fever of 103°F. On physical exam, you see a perforated eardrum that is exuding a small amount of pus. Using a swab, you obtain a sample of the pus and do a Gram stain and culture. The Gram stain reveals small coccobacillary rods. There is no growth on a blood agar plate, but a chocolate agar plate supplemented with X and V factors grows small gray colonies. Which one of the following bacteria is the most likely cause of his otitis media?

(A) Bordetella pertussis

(B) Haemophilus influenzae

(C) Klebsiella pneumoniae

(D) Legionella pneumophila

(E) Pseudomonas aeruginosa

It’s time to play “What’s my name?” I am a small gram-negative rod that causes an important respiratory tract disease. I produce an exotoxin that ADP-ribosylates a G protein. One remarkable feature of my disease is a great increase in lymphocytes. I don’t cause disease commonly in the United States now because of the widespread use of the vaccine that induces antibodies against five of my proteins, one of which is the exotoxin. The identity of the mystery organism is mostly likely which one of the following?

(A) Bordetella pertussis

(B) Haemophilus influenzae

(C) Klebsiella pneumoniae

(D) Legionella pneumophila

(E) Pseudomonas aeruginosa

Your patient is a 75-year-old woman with a 110-pack-year history of cigarette smoking who now has a fever of 39°C and a cough productive of yellowish sputum. Gram stain of the sputum shows small gram-negative rods. There is no growth on blood agar, but colonies do grow on chocolate agar supplemented with hemin and NAD. Which one of the following bacteria is the most likely cause of her pneumonia?

(A) Bordetella pertussis

(B) Haemophilus influenzae

(C) Klebsiella pneumoniae

(D) Legionella pneumophila

(E) Pseudomonas aeruginosa

Your patient is a 5-year-old boy with a high fever and signs of respiratory tract obstruction. Visualization of the epiglottis shows inflammation characterized by marked swelling and “cherry-red” appearance. Which one of the following is the best antibiotic to treat the infection?

(A) Ampicillin

(B) Ceftriaxone

(C) Doxycycline

(D) Gentamicin

(E) Metronidazole

Your patient is a 10-year-old boy who has a high fever and swollen, painful axillary lymph nodes on the left side. His mother says that he brought home a dead rat a few days ago. You suspect he may have bubonic plague. Regarding the causative organism, which one of the following is most accurate?

(A) It has a very low ID₅₀.

(B) It is transmitted from rodents to humans by ticks.

(C) It is endemic primarily in the states along the East Coast of the United States.

(D) Its main virulence factor is an exotoxin that induces interleukin-2 (IL-2) production by CD4-positive helper T cells.

(E) Infection should be treated with high doses of penicillin G intravenously.

Your patient is a 20-year-old man who was bitten on the hand when he tried to break up a fight between two cats yesterday. He now has a red, hot, tender, swollen lesion at the bite site that has spread rapidly across his hand. Which one of the following bacteria is the most likely cause of his cellulitis?

(A) Brucella melitensis

(B) Francisella tularensis

(C) Pasteurella multocida

(D) Yersinia pestis

Your patient is a 30-year-old woman who reports that she has had intermittent fever of 102°F, sweating, and fatigue for the past one month or so. She has lost her appetite and has lost about 10 pounds in that period. She enjoys eating unpasteurized goat cheese. On examination, hepatosplenomegaly is detected. A blood count reveals pancytopenia. Which one of the following bacteria is the most likely cause of this infection?

(A) Brucella melitensis

(B) Francisella tularensis

(C) Pasteurella multocida

(D) Yersinia pestis

Regarding Bartonella henselae, which of the following is most accurate?

(A) Bartonella henselae is an anaerobic, spore-forming, gram-positive rod.

(B) The natural habitat of Bartonella henselae is the cat’s mouth.

(C) Bartonella henselae causes cellulitis in immunocompromised patients such as AIDS patients.

(D) Diagnosis in the clinical laboratory depends on detecting antibodies in the patient’s serum that will agglutinate cardiolipin.

(E) The drug of choice for Bartonella henselae infections is metronidazole.

Your patient is a 25-year-old homeless man who complains of a cough for the past month. The cough is now productive of several tablespoons of blood-streaked sputum per day. The sputum is not foul-smelling. He has lost 10 pounds but says that he doesn’t eat regularly. On physical exam, temperature is 38°C, and coarse rales are heard in the apex of the left lung. An acid-fast stain of the sputum reveals acid-fast rods. Culture of the sputum shows no growth at 7 days, but buff-colored colonies are visible at 21 days. Of the following organisms, which one is most likely to be the cause of this infection?

(A) Mycobacterium fortuitum-chelonae

(B) Mycobacterium leprae

(C) Mycobacterium marinum

(D) Mycobacterium tuberculosis

Your patient is a 25-year-old homeless man who complains of a cough for the past month. The cough is now productive of several tablespoons of blood-streaked sputum per day. The sputum is not foul-smelling. He has lost 10 pounds but says that he doesn’t eat regularly. On physical exam, temperature is 38°C, and coarse rales are heard in the apex of the left lung. An acid-fast stain of the sputum reveals acid-fast rods. Culture of the sputum shows no growth at 7 days, but buff-colored colonies are visible at 21 days. Which one of the following regimens is optimal initial treatment of the patient?

(A) Isoniazid for 9 months

(B) Isoniazid and gentamicin for 2 weeks

(C) Isoniazid and rifampin for 4 months

(D) Isoniazid, rifampin, ethambutol, and pyrazinamide for 2 months

Your patient is a 70-year-old man with progressive weakness in both legs that began about a week ago. He reports back pain and fever for the past month. Magnetic resonance imaging (MRI) of the spine revealed destruction of the seventh thoracic vertebra and a paravertebral mass. Surgical decompression and debridement were performed. Histologic examination of the mass revealed caseating granulomas, and Langhans’ giant cells were observed in the granulomas. Gram stain revealed no organisms, but an acid-fast stain showed red rods. Culture showed no growth at 7 days, but growth was seen at 28 days. Of the following, which one is the most likely cause?

(A) Mycobacterium fortuitum-chelonae

(B) Mycobacterium leprae

(C) Mycobacterium marinum

(D) Mycobacterium tuberculosis

Your patient is a 30-year-old woman who is infected with HIV and has a low CD4 count. She now has the findings of pulmonary tuberculosis, but you are concerned that she may be infected with Mycobacterium avium-intracellulare (MAI). Regarding MAI, which one of the following is most accurate?

(A) Disseminated disease caused by MAI is typically the result of decreased antibody production, whereas disseminated disease caused by M. tuberculosis is typically caused by reduced cell-mediated immunity.

(B) Immigrants from Southeast Asia are more likely to be infected with MAI than with M. tuberculosis.

(C) In the clinical laboratory, MAI forms colonies in 7 days, whereas M. tuberculosis colonies typically require at least 21 days of incubation for colonies to appear.

(D) MAI is typically susceptible to a drug regimen of isoniazid and rifampin, whereas M. tuberculosis is often resistant.

(E) The natural habitat of MAI is the environment, whereas the natural habitat of M. tuberculosis is humans.

Your patient is a 30-year-old woman who is infected with HIV and has a low CD4 count. She now has the findings of pulmonary tuberculosis, but you are concerned that she may be infected with Mycobacterium avium-intracellulare (MAI). If MAI was shown to be the cause of her symptoms, which one of the following is the best choice of antibiotics to prescribe?

(A) Amikacin and doxycycline

(B) Clarithromycin, ethambutol, and rifabutin

(C) Dapsone, rifampin, and clofazimine

(D) Isoniazid and gentamicin

(E) Isoniazid, rifampin, ethambutol, and pyrazinamide

Your patient is a 20-year-old man with a single, slowly expanding, nonpainful scaly lesion on his chest for the past 2 months. The lesion is nonpruritic, and he has lost sensation at the site of the lesion. He is otherwise well. He is a recent immigrant from Central America. An acid-fast stain of a scraping of the lesion is positive. Which one of the following diseases is he most likely to have?

(A) Cutaneous tuberculosis

(B) Fish tank granuloma

(C) Lepromatous leprosy

(D) Scrofula

(E) Tuberculoid leprosy

Your patient is a 75-year-old woman with fever and a painful nodule on her forearm. She also has a nonproductive cough that she says is worse than her usual smoking-related cough. She is taking high-dose corticosteroids (prednisone) for an autoimmune disease. Chest X-ray reveals a nodular lesion in the right upper lobe. A biopsy of the nodule on her arm was obtained. Gram stain of the specimen showed filaments of gram-positive rods. The rods were also weakly acid-fast. Regarding the causative organism, which one of the following is most accurate?

(A) Culture of the organism should be done under anaerobic conditions.

(B) The natural habitat of the organism is the soil.

(C) It produces an exotoxin that inhibits protein synthesis by ADP-ribosylation.

(D) Sulfur granules are often seen in the skin lesion.

(E) The vaccine against this organism contains the capsular polysaccharide as the immunogen.

Your patient is a 20-year-old man who was in a fist fight in a bar about 3 weeks ago. He took a punch that broke his left second molar. He now has a 3-cm inflamed area on the skin overlying the broken tooth that is draining pus. A Gram stain of the pus reveals gram-positive filamentous rods. The rods did not appear red in the acid-fast stain. Regarding the causative organism, which one of the following is most accurate?

(A) Infections caused by this organism occur primarily in the Ohio and Mississippi River Valley area.

(B) The natural habitat of the organism is the soil.

(C) This organism is resistant to both penicillins and aminoglycosides.

(D) Sulfur granules are often seen in the pus located at the orifice of the sinus tract in the skin lesion.

(E) The vaccine against this organism contains a toxoid as the immunogen.

Mycoplasma pneumoniae is an important cause of atypical pneumonia. Regarding this organism, which one of the following is the most accurate?

(A) Amoxicillin is the drug of choice for pneumonia caused by this organism.

(B) Antibody in a patient’s serum will agglutinate human red blood cells at 4°C, but not at 37°C.

(C) Gram stain of the sputum reveals small gram-negative rods.

(D) It is an obligate intracellular parasite that can only grow within human cells in the clinical laboratory.

(E) People with cystic fibrosis are predisposed to pneumonia caused by this organism.

Which one of the following is the drug of choice for atypical pneumonia caused by M. pneumoniae?

(A) Amoxicillin

(B) Azithromycin

(C) Ceftriaxone

(D) Gentamicin

(E) Vancomycin

Your patient is a 65-year-old man with gradually increasing confusion and unsteadiness while walking. A lumbar puncture revealed clear spinal fluid, a normal glucose, and an elevated protein. There were 96 cells/μL, of which 86% were lymphocytes. Gram stain of the cerebrospinal fluid (CSF) was negative. Magnetic resonance imaging (MRI) of the brain was normal. A sample of CSF reacted with beef heart cardiolipin at a titer of 1/1024. Regarding the causative organism of his infection, which one of the following is most accurate?

(A) It is transmitted by tick bite.

(B) Resistance to penicillin G is common, so ceftriaxone should be used.

(C) It has never been grown on bacteriologic media in the clinical laboratory.

(D) It is unlikely to be eradicated because beef cattle are a major reservoir for the organism.

(E) A confirmatory test for this organism utilizes an agglutination reaction with the capsular polysaccharide of the organism.

Your patient is a 20-year-old man with an erythematous, macular, nonpainful rash on the right arm for the past 4 days. The rash is approximately 10 cm in diameter. He also has a fever to 100°F and a mild headache. He reports hiking on several weekends recently in New York State. You suspect the rash is erythema migrans and that he has Lyme disease. Which one of the following is the best approach to confirm your clinical diagnosis?

(A) Detect IgM antibodies in an ELISA assay

(B) Determine the titer in a VDRL test

(C) Gram stain and culture on blood agar incubated aerobically

(D) Gram stain and culture on blood agar incubated anaerobically

(E) Grow on human cells in cell culture and identify with fluorescent antibody

Your patient is a 20-year-old man with an erythematous, macular, nonpainful rash on the right arm for the past 4 days. The rash is approximately 10 cm in diameter. He also has a fever to 100°F and a mild headache. He reports hiking on several weekends recently in New York State. You suspect the rash is erythema migrans and that he has Lyme disease. Assume the patient does have Lyme disease. Which one of the following antibiotics is the most appropriate to treat his infection?

(A) Azithromycin or trimethoprim-sulfamethoxazole

(B) Doxycycline or amoxicillin

(C) Gentamicin or amikacin

(D) Metronidazole or clindamycin

(E) Penicillin G or levofloxacin

Regarding syphilis, which one of the following is most accurate?

(A) The characteristic lesion of primary syphilis is a painful vesicle on the genitals.

(B) In secondary syphilis, the number of organisms is low, so the chance of transmitting the disease to others is low.

(C) In secondary syphilis, both the rapid plasma reagin (RPR) and the fluorescent treponemal antibody-absorbed (FTA-ABS) tests are usually positive.

(D) The antibody titer in the FTA-ABS test typically declines when the patient has been treated adequately.

(E) In congenital syphilis, no antibody is formed against T. pallidum because the fetus is tolerant to the organism.

Regarding Borrelia burgdorferi and Lyme disease, which one of the following is most accurate?

(A) Borrelia burgdorferi infects a larger percentage of the rodent reservoir in western states, such as California, than in northeastern states, such as New York.

(B) Pathogenesis of Lyme disease is based on the production of an exotoxin that induces interleukin-2 production by T-helper cells.

(C) The vaccine against Lyme disease contains the capsular polysaccharide of all four serotypes as the immunogen.

(D) Close family members of those infected with Borrelia burgdorferi should be given ciprofloxacin.

(E) Borrelia burgdorferi is transmitted to humans by the bite of ticks of the genus Ixodes.

Benzathine penicillin G is used to treat primary and secondary syphilis rather than procaine penicillin G. Which one of the following is the best reason for this choice?

(A) Patients allergic to procaine penicillin G are not allergic to benzathine penicillin G.

(B) Benzathine penicillin G has a higher minimal inhibitory concentration than procaine penicillin G.

(C) Benzathine penicillin G penetrates the central nervous system to a greater degree than procaine penicillin G.

(D) Benzathine penicillin G is a depot preparation that provides a long-lasting, high level of drug that kills the slow-growing Treponema pallidum.

Your patient is a 20-year-old man with a urethral discharge. Gram stain of the pus reveals many neutrophils but no bacteria. You suspect this infection may be caused by C. trachomatis. Which one of the following is the laboratory result that best supports your clinical diagnosis?

(A) Gram stain of the pus reveals small gram-positive rods.

(B) The organism produces β-hemolytic colonies on blood agar plates when incubated aerobically.

(C) The organism produces α-hemolytic colonies on blood agar plates when incubated anaerobically.

(D) Fluorescent antibody staining demonstrates cytoplasmic inclusions in epithelial cells in the exudate.

(E) There is a fourfold or greater rise in antibody titer against C. trachomatis.

Regarding chlamydiae, which one of the following is the most accurate?

(A) Lifelong immunity usually follows an episode of disease caused by these organisms.

(B) The reservoir host for the three species of chlamydiae that cause human infection is humans.

(C) Their life cycle consists of elementary bodies outside of cells and reticulate bodies within cells.

(D) They can only replicate within cells because they lack the ribosomes to synthesize their proteins.

(E) The vaccine against C. pneumoniae contains the capsular polysaccharide as the immunogen conjugated to a carrier protein.

Which one of the following is the drug of choice for sexually transmitted disease (urethritis, cervicitis) caused by C. trachomatis?

(A) Ampicillin

(B) Azithromycin

(C) Ciprofloxacin

(D) Metronidazole

(E) Rifampin

Your patient is a 40-year-old woman with the sudden onset of fever to 40°C, severe headache, and petechial rash over most of her body including the palms. Blood cultures are negative. Unfortunately, despite antibiotics and other support, she dies the day after presentation. An autopsy is performed, and immunohistochemical tests on her brain tissue reveal an infection by Rickettsia rickettsii. Of the following, which one is the most accurate?

(A) It is likely she lives in Colorado and was bitten by a tick.

(B) It is likely she lives in Colorado and was bitten by a mosquito.

(C) It is likely she lives in Virginia and was bitten by a tick.

(D) It is likely she lives in Virginia and was bitten by a flea.

(E) It is likely she lives in Connecticut and was bitten by a mosquito.

Regarding Q fever, which one of the following is most accurate?

(A) The causative organism is transmitted by tick bite.

(B) The natural habitat of the causative agent is the white-footed mouse.

(C) The diagnosis is made primarily by Gram stain and culture on chocolate agar.

(D) Occupations that predispose people to Q fever include veterinarians and abattoir workers.

(E) Patients with Q fever often have a petechial rash involving the palms.

Regarding Fusobacterium nucleatum, which one of the following is most accurate?

(A) Its natural habitat is the soil.

(B) It is an anaerobic gram-negative rod with pointed ends.

(C) The drug of choice for infections caused by F. nucleatum is azithromycin.

(D) Laboratory diagnosis is based on detecting the ability of the exotoxin to kill cells in tissue culture.

Regarding Haemophilus ducreyi, which one of the following is most accurate?

(A) It requires both X and V factors to grow on MacConkey’s agar.

(B) Gram stain of exudate from the lesion shows large gram-positive rods.

(C) Penicillin G is the drug of choice to treat infections caused by H. ducreyi.

(D) It causes chancroid, which is characterized by a painful ulcer on the genitals.

Regarding Yersinia enterocolitica, which one of the following is most accurate?

(A) It causes mesenteric adenitis, which can mimic appendicitis.

(B) It is a gram-negative diplococcus found primarily within neutrophils.

(C) It is the most common cause of enterocolitis in the United States.

(D) Its natural habitat is the human oropharynx, and there is no animal reservoir.

Regarding Ehrlichia chaffeensis, which one of the following is most accurate?

(A) It is transmitted primarily by mosquito bite.

(B) It forms β-hemolytic colonies on blood agar.

(C) Its most common clinical presentation is acute meningitis.

(D) It is endemic on the islands off the coast of Massachusetts (e.g., Nantucket).

(E) It forms an inclusion body called a morula in the cytoplasm of infected cell.

An outbreak of sepsis caused by Staphylococcus aureus has occurred in the newborn nursery. You are called upon to investigate. According to your knowledge of the normal flora, what is the MOST likely source of the organism?

(A) Colon

(B) Nose

(C) Throat

(D) Vagina

Each of the statements about the classification of streptococci is correct EXCEPT:

(A) Pneumococci (Streptococcus pneumoniae) are α-hemolytic and can be serotyped on the basis of their polysaccharide capsules.

(B) Enterococci are group D streptococci and can be classified by their ability to grow in 6.5% sodium chloride.

(C) Although pneumococci and the viridans streptococci are α-hemolytic, they can be differentiated by the bile solubility test and their susceptibility to optochin.

(D) Viridans streptococci are identified by Lancefield grouping, which is based on the C carbohydrate in the cell wall.

Each of the following agents is a recognized cause of diarrhea EXCEPT:

(A) Clostridium perfringens

(B) Enterococcus faecalis

(C) Escherichia coli

(D) Vibrio cholerae

Each of the following organisms is an important cause of urinary tract infections EXCEPT:

(A) Escherichia coli

(B) Proteus mirabilis

(C) Klebsiella pneumoniae

(D) Bacteroides fragilis

Your patient is a 30-year-old woman with nonbloody diarrhea for the past 14 hours. Which one of the following organisms is LEAST likely to cause this illness?

(A) Clostridium difficile

(B) Streptococcus pyogenes

(C) Shigella dysenteriae

(D) Salmonella enteritidis

Each of the following statements concerning Mycobacterium tuberculosis is correct EXCEPT:

(A) After being stained with carbolfuchsin, M. tuberculosis resists decolorization with acid alcohol.

(B) Mycobacterium tuberculosis has a large amount of mycolic acid in its cell wall.

(C) Mycobacterium tuberculosis appears as a red rod in Gram-stained specimens.

(D) Mycobacterium tuberculosis appears as a red rod in acid-fast–stained specimens.

A 50-year-old homeless alcoholic has a fever and is coughing up 1 cup of green, foul-smelling sputum per day. You suspect that he may have a lung abscess. Which one of the following pairs of organisms is MOST likely to be the cause?

(A) Listeria monocytogenes and Legionella pneumophila

(B) Nocardia asteroides and Mycoplasma pneumoniae

(C) Fusobacterium nucleatum and Peptostreptococcus intermedius

(D) Clostridium perfringens and Chlamydia psittaci

Which one of the following diseases is BEST diagnosed by serologic means?

(A) Q fever

(B) Pulmonary tuberculosis

(C) Gonorrhea

(D) Actinomycosis

Your patient has subacute bacterial endocarditis caused by a member of the viridans group of streptococci. Which one of the following sites is MOST likely to be the source of the organism?

(A) Skin

(B) Colon

(C) Oropharynx

(D) Urethra

A culture of skin lesions from a patient with pyoderma (impetigo) shows numerous colonies surrounded by a zone of β-hemolysis on a blood agar plate. A Gram-stained smear shows gram-positive cocci. If you found the catalase test to be negative, which one of the following organisms would you MOST probably have isolated?

(A) Streptococcus pyogenes

(B) Staphylococcus aureus

(C) Staphylococcus epidermidis

(D) Streptococcus pneumoniae

The coagulase test, in which the bacteria cause plasma to clot, is used to distinguish:

(A) Streptococcus pyogenes from Enterococcus faecalis

(B) Streptococcus pyogenes from Staphylococcus aureus

(C) Staphylococcus aureus from Staphylococcus epidermidis

(D) Staphylococcus epidermidis from Neisseria meningitidis

Which one of the following is a virulence factor for Staphylococcus aureus?

(A) A heat-labile toxin that inhibits glycine release at the internuncial neuron

(B) An oxygen-labile hemolysin

(C) Resistance to novobiocin

(D) Protein A that binds to the Fc portion of IgG

Which one of the following host defense mechanisms is the MOST important for preventing dysentery caused by Salmonella?

(A) Gastric acid

(B) Salivary enzymes

(C) Normal flora of the mouth

(D) Alpha interferon

The MOST important protective function of the antibody stimulated by tetanus immunization is:

(A) To opsonize the pathogen (Clostridium tetani)

(B) To prevent growth of the pathogen

(C) To prevent adherence of the pathogen

(D) To neutralize the toxin of the pathogen

Five hours after eating reheated rice at a restaurant, a 24-year-old woman and her husband both developed nausea, vomiting, and diarrhea. Which one of the following organisms is the MOST likely to be involved?

(A) Clostridium perfringens

(B) Enterotoxigenic Escherichia coli

(C) Bacillus cereus

(D) Salmonella typhi

Which one of the following bacteria has the LOWEST 50% infectious dose (ID₅₀)?

(A) Shigella sonnei

(B) Vibrio cholerae

(C) Salmonella typhi

(D) Campylobacter jejuni

For which one of the following enteric illnesses is a chronic carrier state MOST likely to develop?

(A) Campylobacter enterocolitis

(B) Shigella enterocolitis

(C) Cholera

(D) Typhoid fever

Which one of the following zoonotic illnesses has NO arthropod vector?

(A) Plague

(B) Lyme disease

(C) Brucellosis

(D) Epidemic typhus

Which one of the following organisms principally infects vascular endothelial cells and as a result often causes a petechial rash?

(A) Salmonella typhi

(B) Rickettsia rickettsii

(C) Haemophilus influenzae

(D) Coxiella burnetii

Which one of the following statements MOST accurately depicts the ability of the organism to be cultured in the laboratory?

(A) Treponema pallidum from a chancre can be grown on a special artificial medium supplemented with cholesterol.

(B) Mycobacterium leprae can be grown in the armadillo and the mouse footpad but not on any artificial media.

(C) Mycobacterium tuberculosis can be grown on enriched artificial media and produces visible colonies in 48 to 96 hours.

(D) Atypical mycobacteria are found widely in soil and water but cannot be cultured on artificial media in the laboratory.

Each of the following statements concerning chlamydiae is correct EXCEPT:

(A) Chlamydiae are strict intracellular parasites because they cannot synthesize sufficient adenosine triphosphate (ATP).

(B) Chlamydiae possess both DNA and RNA and are bounded by a cell wall.

(C) Chlamydia trachomatis has multiple serotypes that can cause different diseases.

(D) Most chlamydiae are transmitted by arthropods.

For which one of the following bacterial vaccines are toxic side effects an important concern?

(A) The vaccine containing pneumococcal polysaccharide

(B) The vaccine containing killed Bordetella pertussis

(C) The vaccine containing tetanus toxoid

(D) The vaccine containing diphtheria toxoid

Each of the following statements concerning Staphylococcus aureus is correct EXCEPT:

(A) Gram-positive cocci in grapelike clusters are seen on Gram-stained smear.

(B) The coagulase test is positive.

(C) Treatment should include a β-lactamase-resistant penicillin.

(D) Endotoxin is an important pathogenetic factor.

Your patient is a 70-year-old man who underwent bowel surgery for colon cancer 3 days ago. He now has a fever and abdominal pain. You are concerned that he may have peritonitis. Which one of the following pairs of organisms is MOST likely to be the cause?

(A) Bacteroides fragilis and Klebsiella pneumoniae

(B) Bordetella pertussis and Salmonella enteritidis

(C) Actinomyces israelii and Campylobacter jejuni

(D) Clostridium botulinum and Shigella dysenteriae

A 65-year-old man develops dysuria and hematuria. A Gram stain of a urine sample shows gram-negative rods. Culture of the urine on EMB agar reveals lactose-negative colonies without evidence of swarming motility. Which one of the following organisms is MOST likely to be the cause of his urinary tract infection?

(A) Enterococcus faecalis

(B) Pseudomonas aeruginosa

(C) Proteus vulgaris

(D) Escherichia coli

A 25-year-old man complains of a urethral discharge. You perform a Gram stain on a specimen of the discharge and see neutrophils but no bacteria. Of the organisms listed, the one MOST likely to cause the discharge is:

(A) Treponema pallidum

(B) Chlamydia trachomatis

(C) Candida albicans

(D) Coxiella burnetii

Two hours after a delicious Thanksgiving dinner of barley soup, roast turkey, stuffing, sweet potato, green beans, cranberry sauce, and pumpkin pie topped with whipped cream, the Smith family of four experience vomiting and diarrhea. Which one of the following organisms is MOST likely to cause these symptoms?

(A) Shigella flexneri

(B) Campylobacter jejuni

(C) Staphylococcus aureus

(D) Salmonella enteritidis

Your patient has a brain abscess that was detected 1 month after a dental extraction. Which one of the following organisms is MOST likely to be involved?

(A) Anaerobic streptococci

(B) Mycobacterium smegmatis

(C) Lactobacillus acidophilus

(D) Mycoplasma pneumoniae

The MOST important contribution of the capsule of Streptococcus pneumoniae to virulence is:

(A) To prevent dehydration of the organisms on mucosal surfaces

(B) To retard phagocytosis by polymorphonuclear leukocytes

(C) To inhibit polymorphonuclear leukocyte chemotaxis

(D) To accelerate tissue invasion by its collagenase-like activity

The MOST important way the host counteracts the function of the pneumococcal polysaccharide capsule is via:

(A) T lymphocytes sensitized to polysaccharide antigens

(B) Polysaccharide-degrading enzymes

(C) Anticapsular antibody

(D) Activated macrophages

The pathogenesis of which one of the following organisms is MOST likely to involve invasion of the intestinal mucosa?

(A) Vibrio cholerae

(B) Shigella sonnei

(C) Enterotoxigenic Escherichia coli

(D) Clostridium botulinum

Which one of the following organisms that infects the gastrointestinal tract is the MOST frequent cause of bacteremia?

(A) Shigella flexneri

(B) Campylobacter jejuni

(C) Vibrio cholerae

(D) Salmonella typhi

A 30-year-old woman with systemic lupus erythematosus is found to have a positive serologic test for syphilis (VDRL test). She denies having had sexual contact with a partner who had symptoms of a venereal disease. The next best step would be to:

(A) Reassure her that the test is a false-positive reaction related to her autoimmune disorder

(B) Trace her sexual contacts for serologic testing

(C) Treat her with penicillin

(D) Perform a fluorescent treponemal antibody-absorbed (FTA-ABS) test on a specimen of her serum

Each of the following statements concerning Treponema is correct EXCEPT:

(A) Treponema pallidum produces an exotoxin that stimulates adenylate cyclase.

(B) Treponema pallidum cannot be grown on conventional laboratory media.

(C) Treponemes are members of the normal flora of the human oropharynx.

(D) Patients infected with T. pallidum produce antibodies that react with beef heart cardiolipin.

Each of the following statements concerning clostridia is correct EXCEPT:

(A) Pathogenic clostridia are found both in the soil and in the normal flora of the colon.

(B) Antibiotic-associated (pseudomembranous) colitis is due to a toxin produced by Clostridium difficile.

(C) Anaerobic conditions at the wound site are not required to cause tetanus, because spores will form in the presence of oxygen.

(D) Botulism, which is caused by ingesting preformed toxin, can be prevented by boiling food prior to eating.

Each of the following statements concerning Bacteroides fragilis is correct EXCEPT:

(A) Bacteroides fragilis is a gram-negative rod that is part of the normal flora of the colon.

(B) Bacteroides fragilis forms endospores, which allow it to survive in the soil.

(C) The capsule of B. fragilis is an important virulence factor.

(D) Bacteroides fragilis infections are characterized by foul-smelling pus.

Each of the following statements concerning staphylococci is correct EXCEPT:

(A) Staphylococcus aureus is differentiated from Staphylococcus epidermidis by the production of coagulase.

(B) Staphylococcus aureus infections are often associated with abscess formation.

(C) The majority of clinical isolates of S. aureus produce penicillinase; therefore, penicillin G should not be used for antibiotic therapy for S. aureus infections.

(D) Scalded skin syndrome caused by S. aureus is due to enzymatic degradation of epidermal desmosomes by catalase.

Acute glomerulonephritis is a nonsuppurative complication that follows infection by which one of the following organisms?

(A) Enterococcus faecalis

(B) Streptococcus pyogenes

(C) Streptococcus pneumoniae

(D) Streptococcus agalactiae

Each of the following statements concerning gram-negative rods is correct EXCEPT:

(A) Escherichia coli is part of the normal flora of the colon; therefore, it does not cause diarrhea.

(B) Escherichia coli ferments lactose, whereas the enteric pathogens Shigella and Salmonella do not.

(C) Klebsiella pneumoniae, although a cause of pneumonia, is part of the normal flora of the colon.

(D) Proteus species are highly motile organisms that are found in the human colon and cause urinary tract infections.

A 70-year-old man is found to have a hard mass in his prostate, which is suspected to be a carcinoma. Twenty-four hours after surgical removal of the mass, he develops fever to 39°C and has several shaking chills. Of the organisms listed, which one is LEAST likely to be involved?

(A) Escherichia coli

(B) Enterococcus faecalis

(C) Klebsiella pneumoniae

(D) Legionella pneumophila

Five days ago, a 65-year-old woman with a lower urinary tract infection began taking ampicillin. She now has a fever and severe diarrhea. Of the organisms listed, which one is MOST likely to be the cause of the diarrhea?

(A) Clostridium difficile

(B) Bacteroides fragilis

(C) Proteus mirabilis

(D) Bordetella pertussis

The pathogenesis of which one of the following diseases does NOT involve an exotoxin?

(A) Scarlet fever

(B) Typhoid fever

(C) Toxic shock syndrome

(D) Botulism

Regarding the effect of benzylpenicillin (penicillin G) on bacteria, which one of the following organisms is LEAST likely to be resistant?

(A) Staphylococcus aureus

(B) Enterococcus faecalis

(C) Streptococcus pyogenes

(D) Neisseria gonorrhoeae

Which one of the following organisms is MOST likely to be the cause of pneumonia in an immunocompetent young adult?

(A) Nocardia asteroides

(B) Serratia marcescens

(C) Mycoplasma pneumoniae

(D) Legionella pneumophila

Each of the following statements concerning chlamydial genital tract infections is correct EXCEPT:

(A) Infection can be diagnosed by finding antichlamydial antibody in a serum specimen.

(B) Infection can persist after administration of penicillin.

(C) Symptomatic infections can be associated with urethral or cervical discharge containing many polymorphonuclear leukocytes.

(D) There is no vaccine against these infections.

Which one of the following illnesses is NOT a zoonosis?

(A) Typhoid fever

(B) Q fever

(C) Tularemia

(D) Rocky Mountain spotted fever

Which one of the following is NOT a characteristic of the Staphylococcus associated with toxic shock syndrome?

(A) Release of a superantigen

(B) Coagulase production

(C) Appearance of the organism in grapelike clusters on Gram-stained smear

(D) Catalase-negative reaction

Which one of the following is NOT an important characteristic of either Neisseria gonorrhoeae or Neisseria meningitidis?

(A) Polysaccharide capsule

(B) IgA protease

(C) M protein

(D) Pili

Which one of the following is NOT an important characteristic of Streptococcus pyogenes?

(A) Protein A

(B) M protein

(C) β-Hemolysin

(D) Polysaccharide group-specific substance

Each of the following is associated with the Lancefield group B streptococci (S. agalactiae) EXCEPT:

(A) Pyoderma (impetigo)

(B) Vaginal carriage in 5% to 25% of normal women of childbearing age

(C) Neonatal sepsis and meningitis

(D) β-Hemolysis

Three organisms, Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae, cause the vast majority of cases of bacterial meningitis. What is the MOST important pathogenic component they share?

(A) Protein A

(B) Capsule

(C) Endotoxin

(D) β-Lactamase

Diarrhea caused by which one of the following agents is characterized by the presence of fecal leukocytes?

(A) Campylobacter jejuni

(B) Rotavirus

(C) Clostridium perfringens

(D) Enterotoxigenic Escherichia coli

Each of the following statements concerning Chlamydia trachomatis is correct EXCEPT:

(A) It is an important cause of nongonococcal urethritis.

(B) It is the cause of lymphogranuloma venereum.

(C) It is an important cause of subacute bacterial endocarditis.

(D) It is an important cause of conjunctivitis.

Each of the following statements concerning Actinomyces and Nocardia is correct EXCEPT:

(A) Actinomysis israelii is an anaerobic rod found as part of the normal flora in the mouth.

(B) Both Actinomyces and Nocardia are branching, filamentous rods.

(C) Nocardia asteroides causes infections primarily in immunocompromised patients.

(D) Infections are usually diagnosed by detecting a significant rise in antibody titer.

Which one of the following types of organisms is NOT an obligate intracellular parasite and therefore can replicate on bacteriologic media?

(A) Chlamydia

(B) Mycoplasma

(C) Adenovirus

(D) Rickettsia

Tissue-degrading enzymes play an important role in the pathogenesis of several bacteria. Which one of the following is NOT involved in tissue or cell damage?

(A) Lecithinase of Clostridium perfringens

(B) Hyaluronidase of Streptococcus pyogenes

(C) M protein of Streptococcus pneumoniae

(D) Leukocidin of Staphylococcus aureus

The soil is the natural habitat for certain microorganisms of medical importance. Which one of the following is LEAST likely to reside there?

(A) Clostridium tetani

(B) Mycobacterium avium-intracellulare

(C) Bacillus anthracis

(D) Chlamydia trachomatis

Which one of the following organisms is the MOST frequent bacterial cause of pharyngitis?

(A) Staphylococcus aureus

(B) Streptococcus pneumoniae

(C) Streptococcus pyogenes

(D) Neisseria meningitidis

Several pathogens are transmitted either during gestation or at birth. Which one of the following is LEAST likely to be transmitted at these times?

(A) Haemophilus influenzae

(B) Treponema pallidum

(C) Neisseria gonorrhoeae

(D) Chlamydia trachomatis

Each of the following statements concerning exotoxins is correct EXCEPT:

(A) Some strains of Escherichia coli produce an enterotoxin that causes diarrhea.

(B) Cholera toxin acts by stimulating adenylate cyclase.

(C) Diphtheria is caused by an exotoxin that inhibits protein synthesis by inactivating an elongation factor.

(D) Botulism is caused by a toxin that hydrolyzes lecithin (lecithinase), thereby destroying nerve cells.

Each of the following statements concerning the VDRL test for syphilis is correct EXCEPT:

(A) The antigen is composed of inactivated Treponema pallidum.

(B) The test is usually positive in secondary syphilis.

(C) False-positive results are more frequent than with the fluorescent treponemal antibody-absorbed (FTA-ABS) test.

(D) The antibody titer declines with appropriate therapy.

Each of the following statements concerning the fluorescent treponemal antibody-absorbed (FTA-ABS) test for syphilis is correct EXCEPT:

(A) The test is specific for Treponema pallidum.

(B) The patient’s serum is absorbed with saprophytic treponemes.

(C) Once positive, the test remains so despite appropriate therapy.

(D) The test is rarely positive in primary syphilis.

Each of the following statements concerning Corynebacterium diphtheriae is correct EXCEPT:

(A) Corynebacterium diphtheriae is a gram-positive rod that does not form spores.

(B) Toxin production is dependent on the organism’s being lysogenized by a bacteriophage.

(C) Diphtheria toxoid should not be given to children younger than 3 years because the incidence of complications is too high.

(D) Antitoxin should be used to treat patients with diphtheria.

Each of the following statements concerning certain gram-negative rods is correct EXCEPT:

(A) Pseudomonas aeruginosa causes wound infections that are characterized by blue-green pus as a result of pyocyanin production.

(B) In unimmunized individuals, invasive disease caused by Haemophilus influenzae is most often due to strains possessing a type b polysaccharide capsule.

(C) Legionella pneumophila infection is acquired by inhalation of aerosols from environmental water sources.

(D) Whooping cough, which is caused by Bordetella pertussis, is on the rise because changing antigenicity of the organism has made the vaccine relatively ineffective.

Each of the following statements concerning enterotoxins is correct EXCEPT:

(A) Enterotoxins typically cause bloody diarrhea with leukocytes in the stool.

(B) Staphylococcus aureus produces an enterotoxin that causes vomiting and diarrhea.

(C) Vibrio cholerae causes cholera by producing an enterotoxin that increases adenylate cyclase activity within the enterocyte.

(D) Escherichia coli enterotoxin mediates ADP-ribosylation of a G protein.

Each of the following statements concerning plague is correct EXCEPT:

(A) Plague is caused by a gram-negative rod that can be cultured on blood agar.

(B) Plague is transmitted from the animal reservoir to humans by flea bite.

(C) The main reservoirs in nature are small rodents.

(D) Plague is of concern in many underdeveloped countries but has not occurred in the United States since 1968.

Which one of the following statements concerning the organisms that cause brucellosis is CORRECT?

(A) Brucellae are transmitted primarily by tick bite.

(B) The principal reservoirs of Brucellae are small rodents.

(C) Brucellae infect reticuloendothelial cells in the liver, spleen, and bone marrow.

(D) Brucellae are obligate intracellular parasites that are usually identified by growth in human cell culture.

Each of the following statements concerning epidemic typhus is correct EXCEPT:

(A) The disease is characterized by a rash.

(B) The Weil-Felix test can aid in diagnosis of the disease.

(C) The disease is caused by a Rickettsia.

(D) The causative organism is transmitted from rodents to humans by a tick.

Which one of the following organisms causes diarrhea by producing an enterotoxin that increases adenylate cyclase activity within enterocytes?

(A) Escherichia coli

(B) Bacteroides fragilis

(C) Staphylococcus aureus

(D) Enterococcus faecalis

Each of the following statements concerning Rocky Mountain spotted fever is correct EXCEPT:

(A) The causative organism forms β-hemolytic colonies on blood agar.

(B) Headache, fever, and rash are characteristic features of the disease.

(C) The disease occurs primarily east of the Mississippi.

(D) The disease is caused by a Rickettsia.

Each of the following statements concerning Clostridium perfringens is correct EXCEPT:

(A) It causes gas gangrene.

(B) It causes food poisoning.

(C) It produces an exotoxin that degrades lecithin and causes necrosis and hemolysis.

(D) It is a gram-negative rod that does not ferment lactose.

Each of the following statements concerning Clostridium tetani is correct EXCEPT:

(A) It is a gram-positive, spore-forming rod.

(B) Pathogenesis is due to the production of an exotoxin that blocks inhibitory neurotransmitters.

(C) It is a facultative organism; it will grow on a blood agar plate in the presence of room air.

(D) Its natural habitat is primarily the soil.

Each of the following statements concerning spirochetes is correct EXCEPT:

(A) Species of Treponema are part of the normal flora of the mouth.

(B) Species of Borrelia cause a tick-borne disease called relapsing fever.

(C) The species of Leptospira that cause leptospirosis grow primarily in humans and are usually transmitted by human-to-human contact.

(D) Species of Treponema cause syphilis and yaws.

Each of the following statements concerning gonorrhea is correct EXCEPT:

(A) Infection in men is more frequently symptomatic than in women.

(B) A presumptive diagnosis can be made by finding gram-negative kidney bean-shaped diplococci within neutrophils in a urethral discharge.

(C) The definitive diagnosis can be made by detecting antibodies to Neisseria gonorrhoeae in the patient’s serum.

(D) Gonococcal conjunctivitis of the newborn rarely occurs in the United States, because silver nitrate or erythromycin is commonly used as prophylaxis.

Each of the following statements concerning Mycobacterium tuberculosis is correct EXCEPT:

(A) Some strains of M. tuberculosis isolated from patients exhibit multiple drug resistance (i.e., they are resistant to both isoniazid and rifampin).

(B) Mycobacterium tuberculosis contains a small amount of lipid in its cell wall and therefore stains poorly with the Gram stain.

(C) Mycobacterium tuberculosis grows slowly, often requiring 3 to 6 weeks before colonies appear.

(D) The antigen in the tuberculin skin test is a protein extracted from the organism.

Which one of the following statements concerning immunization against diseases caused by clostridia is CORRECT?

(A) Antitoxin against tetanus protects against botulism as well, because the two toxins share antigenic sites.

(B) Vaccines containing alpha toxin (lecithinase) are effective in protecting against gas gangrene.

(C) The toxoid vaccine against Clostridium difficile infection should be administered to immunocompromised patients.

(D) Immunization with tetanus toxoid induces effective protection against tetanus toxin.

Each of the following statements concerning neisseriae is correct EXCEPT:

(A) They are gram-negative diplococci.

Part II: Clinical Bacteriology

Send Email

Citation

Jump to a Section

Part II: Clinical Bacteriology