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

Part I: Basic Bacteriology

You’re watching a television program that is discussing viruses called bacteriophages that can kill bacteria. Your roommate says, “Wow, maybe viruses can be used to kill the bacteria that infect people! You’re taking the Microbiology course now; what’s the difference between viruses and bacteria?” Which one of the following would be the most accurate statement to make?

(A) Viruses do not have mitochondria, whereas bacteria do.

(B) Viruses do not have a nucleolus, whereas bacteria do.

(C) Viruses do not have ribosomes, whereas bacteria do.

(D) Viruses replicate by binary fission, whereas bacteria replicate by mitosis.

(E) Viruses are prokaryotic, whereas bacteria are eukaryotic.

Bacteria, fungi (yeasts and molds), viruses, and protozoa are important causes of human disease. Which one of the following microbes contains either DNA or RNA but not both?

(A) Bacteria

(B) Molds

(C) Protozoa

(D) Viruses

(E) Yeasts

Which one of the following contains DNA that is not surrounded by a nuclear membrane?

(A) Bacteria

(B) Molds

(C) Protozoa

(D) Yeasts

The initial step in the process of many bacterial infections is adherence of the organism to mucous membranes. The bacterial component that mediates adherence is the:

(A) lipid A

(B) nucleoid

(C) peptidoglycan

(D) pilus

(E) plasmid

In the Gram stain procedure, bacteria are exposed to 95% alcohol or to an acetone/alcohol mixture. The purpose of this step is:

(A) to adhere the cells to the slide

(B) to retain the purple dye within all the bacteria

(C) to disrupt the outer cell membrane so the purple dye can leave the bacteria

(D) to facilitate the entry of the purple dye into the gram-negative cells

(E) to form a complex with the iodine solution

In the process of studying how bacteria cause disease, it was found that a rare mutant of a pathogenic strain failed to form a capsule. Which one of the following statements is the most accurate in regard to this unencapsulated mutant strain?

(A) It was nonpathogenic primarily because it was easily phagocytized.

(B) It was nonpathogenic primarily because it could not invade tissue.

(C) It was nonpathogenic primarily because it could only grow anaerobically.

(D) It was highly pathogenic because it could secrete larger amounts of exotoxin.

(E) It was highly pathogenic because it could secrete larger amounts of endotoxin.

Mycobacterium tuberculosis stains well with the acid-fast stain, but not with the Gram stain. Which one of the following is the most likely reason for this observation?

(A) It has a large number of pili that absorb the purple dye.

(B) It has a large amount of lipid that prevents entry of the purple dye.

(C) It has a very thin cell wall that does not retain the purple dye.

(D) It is too thin to be seen in the Gram stain.

(E) It has histones that are highly negatively charged.

Of the following bacterial components, which one exhibits the most antigenic variation?

(A) Capsule

(B) Lipid A of endotoxin

(C) Peptidoglycan

(D) Ribosome

(E) Spore

β-Lactamases are an important cause of antibiotic resistance. Which one of the following is the most common site where β-lactamases are located?

(A) Attached to DNA in the nucleoid

(B) Attached to pili on the bacterial surface

(C) Free in the cytoplasm

(D) Within the capsule

(E) Within the periplasmic space

Which one of the following is the most accurate description of the structural differences between gram-positive bacteria and gram-negative bacteria?

(A) Gram-positive bacteria have a thick peptidoglycan layer, whereas gram-negative bacteria have a thin layer.

(B) Gram-positive bacteria have an outer lipid-rich membrane, whereas gram-negative bacteria do not.

(C) Gram-positive bacteria form a sex pilus that mediates conjugation, whereas gram-negative bacteria do not.

(D) Gram-positive bacteria have plasmids, whereas gram-negative bacteria do not.

(E) Gram-positive bacteria have capsules, whereas gram-negative bacteria do not.

Bacteria that cause nosocomial (hospital-acquired) infections often produce extracellular substances that allow them to stick firmly to medical devices, such as intravenous catheters. Which one of the following is the name of this extracellular substance?

(A) Axial filament

(B) Endotoxin

(C) Flagella

(D) Glycocalyx

(E) Porin

Lysozyme in tears is an effective mechanism for preventing bacterial conjunctivitis. Which one of the following bacterial structures does lysozyme degrade?

(A) Endotoxin

(B) Nucleoid DNA

(C) Peptidoglycan

(D) Pilus

(E) Plasmid DNA

Several bacteria that form spores are important human pathogens. Which one of the following is the most accurate statement about bacterial spores?

(A) They are killed by boiling for 15 minutes.

(B) They are produced primarily by gram-negative cocci.

(C) They are formed primarily when the bacterium is exposed to antibiotics.

(D) They are produced by anaerobes only in the presence of oxygen.

(E) They are metabolically inactive yet can survive for years in that inactive state.

Figure 3–1 depicts a bacterial growth curve divided into phases a, b, c, and d. In which one of the phases are antibiotics such as penicillin most likely to kill bacteria?

FIGURE 3–1. Growth curve of bacteria: a, lag phase; b, log phase; c, stationary phase; d, death phase. (Reproduced with permission from Joklik WK et al. Zinsser Microbiology. 20th ed. Originally published by Appleton & Lange. Copyright 1992, McGraw-Hill.)

(A) Phase a

(B) Phase b

(C) Phase c

(D) Phase d

Some bacteria are obligate anaerobes. Which of the following statements best explains this phenomenon?

(A) They can produce energy both by fermentation (i.e., glycolysis) and by respiration using the Krebs cycle and cytochromes.

(B) They cannot produce their own ATP.

(C) They do not form spores.

(D) They lack superoxide dismutase and catalase.

(E) They do not have a capsule.

The emergence of antibiotic-resistant bacteria, especially in enteric gram-negative rods, is a medically important phenomenon. This most commonly occurs by a process that involves a sex pilus and the subsequent transfer of plasmids carrying one or more transposons. Which one of the following is the name that best describes this process?

(A) Conjugation

(B) Transduction

(C) Transformation

(D) Translocation

(E) Transposition

Several important pathogenic bacteria have the ability to translocate pieces of their DNA in a process called programmed rearrangements. Which one of the following is the most important known consequence of this ability?

(A) The number of plasmids increases significantly, which greatly enhances antibiotic resistance.

(B) The amount of endotoxin increases significantly, which greatly enhances the ability to cause septic shock.

(C) The surface antigens of the bacteria vary significantly, which greatly enhances the ability to avoid opsonization by antibody.

(D) The ability of the bacterium to be lysogenized is significantly increased, which greatly enhances the ability to produce increased amounts of exotoxins.

(E) The ability of the bacterium to survive intracellularly is greatly increased.

Which statement is the most accurate regarding transposons?

(A) They encode enzymes that degrade the ends of the bacterial chromosome.

(B) They are short sequences of DNA that often encode enzymes that mediate antibiotic resistance.

(C) They are short sequences of RNA that silence specific regulatory genes.

(D) They are a family of transfer RNAs that enhance mutations at “hot spots” in the bacterial genome.

Corynebacterium diphtheriae causes the disease diphtheria by producing diphtheria toxin. The gene encoding the toxin is integrated into bacterial genome during lysogenic conversion. The toxin gene was acquired by which process?

(A) Conjugation

(B) Transduction

(C) Transformation

(D) Translocation

(E) Transposition

The colon is the site of the largest number of normal flora bacteria. Which of the following bacteria is found in the greatest number in the colon?

(A) Bacteroides fragilis

(B) Clostridium perfringens

(C) Enterococcus faecalis

(D) Escherichia coli

(E) Lactobacillus species

A 76-year-old woman with a prosthetic (artificial) hip comes to you complaining of fever and pain in that joint. You are concerned about an infection by S. epidermidis. Using your knowledge of normal flora, what is the most likely source of this organism?

(A) Dental plaque

(B) Mouth

(C) Skin

(D) Stomach

(E) Vagina

Your patient is a 30-year-old woman with a previous history of rheumatic fever who has had fever for the past 2 weeks. On examination, you find a new heart murmur. You suspect endocarditis and do a blood culture, which grows a viridans group Streptococcus later identified as S. sanguinis. Using your knowledge of normal flora, what is the most likely source of this organism?

(A) Duodenum

(B) Skin

(C) Throat

(D) Urethra

(E) Vagina

An outbreak of postsurgical wound infections caused by S. aureus has occurred in the hospital. The infection control team was asked to determine whether the organism could be carried by one of the operating room personnel. Using your knowledge of normal flora, which of the following body sites is the most likely location for this organism?

(A) Colon

(B) Gingival crevice

(C) Mouth

(D) Nose

(E) Throat

Handwashing is an important means of interrupting the chain of transmission from one person to another. Infection by which of the following bacteria is most likely to be interrupted by handwashing?

(A) Borrelia burgdorferi

(B) Legionella pneumophila

(C) Staphylococcus aureus

(D) Streptococcus agalactiae (group B Streptococcus)

(E) Treponema pallidum

Vertical transmission is the transmission of organisms from mother to fetus or newborn child. Infection by which of the following bacteria is most likely to be transmitted vertically?

(A) Chlamydia trachomatis

(B) Clostridium tetani

(C) Haemophilus influenzae

(D) Shigella dysenteriae

(E) Streptococcus pneumoniae

The cells involved with pyogenic inflammation are mainly neutrophils, whereas the cells involved with granulomatous inflammation are mainly macrophages and helper T cells. Infection by which of the following bacteria is most likely to elicit granulomatous inflammation?

(A) Escherichia coli

(B) Mycobacterium tuberculosis

(C) Neisseria gonorrhoeae

(D) Streptococcus pyogenes

(E) Staphylococcus aureus

Which of the following sets of properties of exotoxins and endotoxins is correctly matched?

(A) Exotoxins—polypeptides; endotoxins—lipopolysaccharide

(B) Exotoxins—weakly antigenic; endotoxins—highly antigenic

(C) Exotoxins—produced only by gram-negative bacteria; endotoxins—produced only by gram-positive bacteria

(D) Exotoxins—weakly toxic per microgram; endotoxins—highly toxic per microgram

(E) Exotoxins—toxoid vaccines are ineffective; endotoxins—toxoid vaccines are effective

Which of the following sets consists of bacteria both of which produce exotoxins that increase cyclic AMP within human cells?

(A) Vibrio cholerae and Corynebacterium diphtheriae

(B) Clostridium perfringens and Streptococcus pyogenes

(C) Escherichia coli and Bordetella pertussis

(D) Corynebacterium diphtheriae and Staphylococcus aureus

(E) Bacillus anthracis and Staphylococcus epidermidis

Which of the following sets of bacteria produces exotoxins that act by ADP-ribosylation?

(A) Corynebacterium diphtheriae and Escherichia coli

(B) Clostridium perfringens and Staphylococcus aureus

(C) Clostridium tetani and Bacillus anthracis

(D) Enterococcus faecalis and Mycobacterium tuberculosis

(E) Escherichia coli and Streptococcus pyogenes

Which of the following bacteria produces an exotoxin that inhibits the release of acetylcholine at the neuromuscular junction?

(A) Bacillus anthracis

(B) Bordetella pertussis

(C) Clostridium botulinum

(D) Corynebacterium diphtheriae

(E) Escherichia coli

A 25-year-old man with abdominal pain was diagnosed with acute appendicitis. He then had a sudden rise in temperature to 39°C and a sudden fall in blood pressure. Which of the following is the most likely cause of the fever and hypotension?

(A) An exotoxin that ADP-ribosylates elongation factor-2

(B) An exotoxin that stimulates production of large amounts of cyclic AMP

(C) An endotoxin that causes release of tumor necrosis factor

(D) An endotoxin that binds to a class I MHC protein

(E) An exoenzyme that cleaves hyaluronic acid

Several biotech companies have sponsored clinical trials of a drug consisting of monoclonal antibody to lipid A. Sepsis caused by which of the following sets of bacteria is most likely to be improved following administration of this antibody?

(A) Bordetella pertussis and Clostridium perfringens

(B) Escherichia coli and Neisseria meningitidis

(C) Pseudomonas aeruginosa and Bacillus anthracis

(D) Staphylococcus epidermidis and Staphylococcus aureus

(E) Streptococcus pneumoniae and Staphylococcus aureus

Regarding endotoxin, which of the following is the MOST accurate?

(A) Endotoxin is a polypeptide, the toxic portion of which consists of two D-alanines.

(B) Endotoxin is produced by both gram-positive cocci and gram-negative cocci.

(C) Endotoxin acts by binding to class II MHC proteins and the variable portion of the beta chain of the T-cell receptor.

(D) Endotoxin causes fever and hypotension by inducing the release of interleukins such as interleukin-1 and tumor necrosis factor.

(E) The antigenicity of endotoxin resides in its fatty acid side chains.

Which one of the following host defense processes is the MOST important in preventing the action of exotoxins?

(A) Binding of cytokines to exotoxin-specific receptors inhibits the attachment of exotoxins.

(B) Degradation of exotoxins by the membrane attack complex of complement.

(C) Lysis of exotoxins by perforins produced by cytotoxic T cells.

(D) Neutralization of exotoxins by antibody prevents binding to target cell membrane.

(E) Phagocytosis of exotoxins by neutrophils and subsequent destruction by hypochlorite.

An inflammatory response in the skin is characterized by erythema (redness). Which of the following is the most important cause of this erythema?

(A) C3b component of complement

(B) Gamma interferon

(C) Histamine

(D) Hypochlorite

(E) Superoxide

A 1-year-old child with repeated infections was diagnosed with chronic granulomatous disease (CGD). A defect in which of the following is the cause of CGD?

(A) Gamma interferon receptor

(B) LFA-integrins

(C) Mannose-binding protein

(D) NADPH oxidase

(E) Nitric oxide

Opsonization is the process by which:

(A) Bacteria are made more easily phagocytized.

(B) Chemokines attract neutrophils to the site of infection.

(C) Neutrophils migrate from the blood through the endothelium to reach the site of infection.

(D) The acute-phase response is induced.

(E) The alternate pathway of complement is activated.

If the venipuncture site is inadequately disinfected, blood cultures are most often contaminated with which of the following bacteria?

(A) Escherichia coli

(B) Haemophilus influenzae

(C) Pseudomonas aeruginosa

(D) Staphylococcus epidermidis

(E) Streptococcus pneumoniae

The main purpose of performing a throat culture is to detect the presence of which of the following bacteria?

(A) Neisseria meningitidis

(B) Staphylococcus aureus

(C) Staphylococcus epidermidis

(D) Streptococcus pneumoniae

(E) Streptococcus pyogenes

A sputum culture will be rejected (i.e., it will not be stained or cultured) by the clinical laboratory if:

(A) it is streaked with blood.

(B) it contains IgA antibody.

(C) it contains many more epithelial cells than neutrophils.

(D) it contains pus.

(E) it contains sulfur granules.

The identification of Salmonella and Shigella in stool cultures using eosin-methylene blue (EMB) media is dependent on which of the following properties?

(A) Salmonella and Shigella produce a blue colony in the presence of methylene blue.

(B) Salmonella and Shigella produce a colorless colony because they do not ferment lactose.

(C) Salmonella and Shigella produce a green colony because they use the bile in the media.

(D) Salmonella and Shigella produce a red colony in the presence of eosin.

(E) Salmonella and Shigella produce a yellow colony because they ferment glucose.

Cefazolin is often given prior to surgery to prevent postsurgical wound infections. Which of the following best describes the mode of action of cefazolin?

(A) It acts as an electron sink depriving the bacteria of reducing power.

(B) It binds to the 30S ribosome and inhibits bacterial protein synthesis.

(C) It inhibits transcription of bacterial mRNA.

(D) It inhibits transpeptidases needed to synthesize pepti-doglycan.

(E) It inhibits folic acid synthesis needed to act as a methyl donor.

Which of the following drugs inhibits bacterial nucleic acid synthesis by blocking the production of tetrahydrofolic acid?

(A) Ceftriaxone

(B) Erythromycin

(C) Metronidazole

(D) Rifampin

(E) Trimethoprim

Regarding both penicillins and aminoglycosides, which of the following is the most accurate?

(A) Both act at the level of the cell wall.

(B) Both are bactericidal drugs.

(C) Both require an intact β-lactam ring for their activity.

(D) Both should not be given to children under the age of 8 years because damage to cartilage can occur.

(E) They should not be given together because they are antagonistic.

Listed below are drug combinations that are used to treat certain infections. Which of the following is a combination in which both drugs act to inhibit the same metabolic pathway?

(A) Ceftriaxone and azithromycin

(B) Isoniazid and rifampin

(C) Penicillin G and gentamicin

(D) Sulfonamide and trimethoprim

Regarding penicillins and cephalosporins, which of the following is the most accurate?

(A) Cleavage of the β-lactam ring will inactivate penicillins but not cephalosporins.

(B) Penicillins act by inhibiting transpeptidases but cephalosporins do not.

(C) Penicillins and cephalosporins are both bactericidal drugs.

(D) Penicillins and cephalosporins are active against gram-positive cocci but not against gram-negative rods.

(E) Renal tubule damage is an important adverse effect caused by both penicillins and cephalosporins.

Regarding antimicrobial drugs that act by inhibiting nucleic acid synthesis in bacteria, which of the following is the most accurate?

(A) Ciprofloxacin inhibits RNA polymerase by acting as a nucleic acid analogue.

(B) Rifampin inhibits the synthesis of messenger RNA.

(C) Sulfonamides inhibit DNA synthesis by chain termination of the elongating strand.

(D) Trimethoprim inhibits DNA polymerase by preventing the unwinding of double-stranded DNA.

Regarding aminoglycosides and tetracyclines, which of the following is the most accurate?

(A) Both classes of drugs are bactericidal.

(B) Both classes of drugs inhibit protein synthesis by binding to the 30S ribosomal subunit.

(C) Both classes of drugs inhibit peptidyl transferase, the enzyme that synthesizes the peptide bond.

(D) Both classes of drugs must be acetylated within human cells to form the active antibacterial compound.

(E) Both classes of drugs cause brown staining of teeth when administered to young children.

The next three questions ask about the adverse effects of antibiotics, which are an important consideration when deciding which antibiotic to prescribe. Which antibiotic causes significant neurotoxicity and must be taken in conjunction with pyridoxine (vitamin B₆) to prevent these neurologic complications?

(A) Amoxicillin

(B) Ceftriaxone

(C) Isoniazid

(D) Rifampin

(E) Vancomycin

Of the following antibiotics, which causes the most phototoxicity (rash when exposed to sunlight)?

(A) Nafcillin

(B) Ciprofloxacin

(C) Gentamicin

(D) Metronidazole

(E) Sulfamethoxazole

Which of the following antibiotics causes “red man” syndrome?

(A) Azithromycin

(B) Doxycycline

(C) Gentamicin

(D) Sulfamethoxazole

(E) Vancomycin

The spread of antibiotic resistance from one bacterium to another is a well-recognized and clinically important phenomenon. Which one of the following mechanisms is most likely to be involved with the spread of resistance?

(A) Acetylation

(B) Conjugation

(C) Programmed rearrangement

(D) Protoplast mobility

(E) Translation

Regarding the specific mechanisms by which bacteria become resistant to antimicrobial drugs, which one of the following is the most accurate?

(A) Some bacteria contain an enzyme that cleaves the ring of aminoglycosides.

(B) Some bacteria contain clavulanic acid, which binds to penicillin G and inactivates it.

(C) Some bacteria contain a mutated gene encoding an altered transpeptidase, which makes them resistant to doxycycline.

(D) Some bacteria contain a mutated gene that encodes an altered RNA polymerase, which makes them resistant to rifampin.

(E) Some bacteria contain an altered ribosomal protein, which makes them resistant to isoniazid.

The susceptibility of bacteria to an antibiotic is often determined by using the minimal inhibitory concentration (MIC) assay. Regarding the MIC assay, which one of the following is the most accurate?

(A) MIC is the lowest concentration of the bacteria isolated from the patient that inhibits the activity of a standard dose of antibiotic.

(B) MIC is the lowest concentration of antibiotic that inhibits the growth of the bacteria isolated from the patient.

(C) MIC is the lowest concentration of antibiotic that kills the bacteria isolated from the patient.

(D) MIC is the lowest concentration of antibiotic in the patient’s serum that inhibits the activity of a standard dose of antibiotic.

The MIC of the patient’s organism to penicillin is 1 μg/mL and the MIC to gentamicin is 8 μg/mL. However, the MIC to a combination of penicillin and gentamicin is 0.01 μg/mL. Which one of the following terms is the most accurate to describe this effect?

(A) Activation

(B) Antagonism

(C) Reassortment

(D) Recombination

(E) Synergism

Regarding the mechanisms of resistance to specific drugs, which one of the following is the most accurate?

(A) Certain strains of Enterococcus faecalis produce D-lactate rather than D-alanine, which causes them to be resistant to vancomycin.

(B) Certain strains of Escherichia coli produce ergosterol, which causes them to be resistant to gentamicin.

(C) Certain strains of Neisseria gonorrhoeae produce a mutant peptidyl transferase, which causes them to be resistant to tetracycline.

(D) Certain strains of Streptococcus pyogenes produce a β-lactamase, which causes them to be resistant to erythromycin.

Which one of the following is the immunogen in the vaccine against Streptococcus pneumoniae?

(A) Capsular polysaccharide

(B) Endotoxin

(C) Formaldehyde-killed organisms

(D) Pilus protein

(E) Toxoid

(F) Factor H binding protein

Disease caused by which one of the following bacteria is prevented by a toxoid vaccine?

(A) Bacteroides fragilis

(B) Corynebacterium diphtheriae

(C) Neisseria meningitidis

(D) Salmonella typhi

(E) Vibrio cholerae

Disease caused by which one of the following bacteria is prevented by a vaccine in which the immunogen is covalently bound to a carrier protein (conjugate vaccine)?

(A) Bacillus anthracis

(B) Clostridium tetani

(C) Haemophilus influenzae

(D) Mycobacterium tuberculosis

(E) Streptococcus pyogenes

Which one of the following is the immunogen in the vaccine against group B Neisseria meningitidis?

(A) Capsular polysaccharide

(B) Endotoxin

(C) Formaldehyde-killed organisms

(D) Pilus protein

(E) Toxoid

(F) Factor H binding protein

Passive immunity is used to prevent or treat disease caused by which one of the following sets of bacteria?

(A) Clostridium tetani and Clostridium botulinum

(B) Escherichia coli and Staphylococcus aureus

(C) Neisseria meningitidis and Bacillus anthracis

(D) Streptococcus pneumoniae and Haemophilus influenzae

(E) Streptococcus pyogenes and Salmonella typhi

Regarding sterilization and disinfection, which one of the following is the most accurate statement?

(A) Seventy percent alcohol is a better antiseptic than iodine, so 70% alcohol should be used to disinfect the skin prior to drawing a blood culture rather than iodine.

(B) Disinfectants kill both bacterial cells and bacterial spores.

(C) During sterilization by autoclaving, the temperature must be raised above boiling in order to kill bacterial spores.

(D) Transmission of milk-borne diseases can be prevented by pasteurization, which kills both bacterial cells and spores.

(E) Ultraviolet light used in the operating room to disinfect the room kills bacteria primarily by causing oxidation of lipids in the cell membrane.

Which one of the following chemicals is used to sterilize heat-sensitive materials, such as surgical instruments, in the hospital?

(A) Benzalkonium chloride

(B) Phenol

(C) Ethylene oxide

(D) Thimerosal

(E) Tincture of iodine

Each of the following statements concerning the surface structures of bacteria is correct EXCEPT:

(A) Pili mediate the interaction of bacteria with mucosal epithelium.

(B) Polysaccharide capsules retard phagocytosis.

(C) Both gram-negative rods and cocci have lipopolysaccharide (“endotoxin”) in their cell wall.

(D) Bacterial flagella are nonantigenic in humans because they closely resemble human flagella in chemical composition.

Each of the following statements concerning peptidoglycan is correct EXCEPT:

(A) It has a backbone composed of alternating units of muramic acid and acetylglucosamine.

(B) Cross-links between the tetrapeptides involve D-alanine.

(C) It is thinner in gram-positive than in gram-negative cells.

(D) It can be degraded by lysozyme.

Each of the following statements concerning bacterial spores is correct EXCEPT:

(A) Their survival ability is based on their enhanced metabolic activity.

(B) They are formed by gram-positive rods.

(C) They can be killed by being heated in an autclave to 121°C for 15 minutes.

(D) They are formed primarily when nutrients are limited.

Which one of the statements is the MOST accurate comparison of human, bacterial, and fungal cells?

(A) Human cells undergo mitosis, whereas neither bacteria nor fungi do.

(B) Human and fungal cells have a similar cell wall, in contrast to bacteria, whose cell wall contains peptidoglycan.

(C) Human and bacterial cells have plasmids, whereas fungal cells do not.

(D) Human and fungal cells have similar ribosomes, whereas bacterial ribosomes are significantly different.

Which statement is MOST accurate regarding the drug depicted in the diagram?

(A) It inhibits DNA synthesis.

(B) It is bacteriostatic.

(C) It binds to 30S ribosomes.

(D) It prevents formation of folic acid.

Each of the following statements regarding the selective action of antibiotics on bacteria is correct EXCEPT:

(A) Chloramphenicol affects the large subunit of the bacterial ribosome, which is different from the large subunit of the human ribosome.

(B) Isoniazid affects the DNA polymerase of bacteria but not that of human cells.

(C) Sulfonamides affect folic acid synthesis in bacteria, a pathway that does not occur in human cells.

(D) Penicillins affect bacteria rather than human cells because bacteria have a cell wall, whereas human cells do not.

Each of the following statements concerning endotoxins is correct EXCEPT:

(A) They are less toxic (i.e., less active on a weight basis) than exotoxins.

(B) They are more stable on heating than exotoxins.

(C) They bind to specific cell receptors, whereas exotoxins do not.

(D) They are part of the bacterial cell wall, whereas exotoxins are not.

The MAIN host defense against bacterial exotoxins is:

(A) Activated macrophages secreting proteases

(B) IgG and IgM antibodies

(C) Helper T cells

(D) Modulation of host cell receptors in response to the toxin

Which one of the following processes involves a sex pilus?

(A) Transduction of a chromosomal gene

(B) Transposition of a mobile genetic element

(C) Integration of a temperate bacteriophage

(D) Conjugation resulting in transfer of an R (resistance) factor

Each of the following statements concerning the normal flora is correct EXCEPT:

(A) The most common organism found on the skin is Staphylococcus epidermidis.

(B) Escherichia coli is a prominent member of the normal flora of the throat.

(C) The major site where Bacteroides fragilis is found is the colon.

(D) One of the most common sites where Staphylococcus aureus is found is the nose.

Each of the following statements concerning the mechanism of action of antimicrobial drugs is correct EXCEPT:

(A) Vancomycin acts by inhibiting peptidoglycan synthesis.

(B) Quinolones, such as ciprofloxacin, act by inhibiting the DNA gyrase of bacteria.

(C) Erythromycin is a bactericidal drug that disrupts cell membranes by a detergent-like action.

(D) Aminoglycosides such as streptomycin are bactericidal drugs that inhibit protein synthesis.

Each of the following statements concerning the resistance of bacteria to antimicrobial drugs is correct EXCEPT:

(A) Resistance to chloramphenicol is known to be due to an enzyme that acetylates the drug.

(B) Resistance to penicillin is known to be due to reduced affinity of transpeptidases.

(C) Resistance to penicillin is known to be due to cleavage by β-lactamase.

(D) Resistance to tetracycline is known to be due to an enzyme that hydrolyzes the ester linkage.

Of the following choices, the MOST important function of antibody in host defenses against bacteria is:

(A) Activation of lysozyme that degrades the cell wall

(B) Acceleration of proteolysis of exotoxins

(C) Facilitation of phagocytosis

(D) Inhibition of bacterial protein synthesis

Which of the following events is MOST likely to be due to bacterial conjugation?

(A) A strain of Corynebacterium diphtheriae produces a toxin encoded by a prophage.

(B) A strain of Pseudomonas aeruginosa produces β-lactamase encoded by a plasmid similar to a plasmid of another gram-negative organism.

(C) An encapsulated strain of Streptococcus pneumoniae acquires the gene for capsule formation from an extract of DNA from another encapsulated strain.

(D) A gene encoding resistance to gentamicin in the Escherichia coli chromosome appears in the genome of a bacteriophage that has infected E. coli.

Which one of the following BEST describes the mode of action of endotoxin?

(A) Degrades lecithin in cell membranes

(B) Inactivates elongation factor-2

(C) Blocks release of acetylcholine

(D) Causes the release of tumor necrosis factor

The identification of bacteria by serologic tests is based on the presence of specific antigens. Which one of the following bacterial components is LEAST likely to contain useful antigens?

(A) Capsule

(B) Flagella

(C) Exotoxins

(D) Ribosomes

Each of the following statements concerning bacterial spores is correct EXCEPT:

(A) Spores are formed under adverse environmental conditions such as the absence of a carbon source.

(B) Spores are resistant to boiling.

(C) Spores are metabolically inactive and contain dipicolinic acid, a calcium chelator.

(D) Spores are formed primarily by organisms of the genus Neisseria.

Each of the following statements concerning the mechanism of action of antibacterial drugs is correct EXCEPT:

(A) Cephalosporins are bactericidal drugs that inhibit the transpeptidase reaction and prevent cell wall synthesis.

(B) Tetracyclines are bacteriostatic drugs that inhibit protein synthesis by blocking tRNA binding.

(C) Aminoglycosides are bacteriostatic drugs that inhibit protein synthesis by activating ribonuclease, which degrades mRNA.

(D) Erythromycin is a bacteriostatic drug that inhibits protein synthesis by blocking translocation of the polypeptide.

Each of the following is a typical property of obligate anaerobes EXCEPT:

(A) They generate energy by using the cytochrome system.

(B) They grow best in the absence of air.

(C) They lack superoxide dismutase.

(D) They lack catalase.

Each of the following statements concerning the Gram stain is correct EXCEPT:

(A) Escherichia coli stains pink because it has a thin peptidoglycan layer.

(B) Streptococcus pyogenes stains blue because it has a thick peptidoglycan layer.

(C) Mycobacterium tuberculosis stains blue because it has a thick lipid layer.

(D) Mycoplasma pneumoniae is not visible in the Gram stain because it does not have a cell wall.

Each of the following statements concerning the killing of bacteria is correct EXCEPT:

(A) Lysozyme in tears can hydrolyze bacterial cell walls.

(B) Silver nitrate can inactivate bacterial enzymes.

(C) Detergents can disrupt bacterial cell membranes.

(D) Ultraviolet light can degrade bacterial capsules.

In the Gram stain, the decolorization of gram-negative bacteria by acetone-alcohol is MOST closely related to:

(A) Proteins encoded by F plasmids

(B) Lipids in the outer cell membrane

(C) 70S ribosomes

(D) Branched polysaccharides in the capsule

Chemical modification of benzylpenicillin (penicillin G) has resulted in several beneficial changes in the clinical use of this drug. Which one of the following is NOT one of those beneficial changes?

(A) Lowered frequency of anaphylaxis

(B) Increased activity against gram-negative rods

(C) Increased resistance to stomach acid

(D) Reduced cleavage by penicillinase

Each of the following statements concerning resistance to antibiotics is correct EXCEPT:

(A) Resistance to aminoglycosides can be due to phosphorylating enzymes encoded by R plasmids.

(B) Resistance to sulfonamides can be due to enzymes that hydrolyze the five-membered ring structure.

(C) Resistance to penicillins can be due to alterations in binding proteins in the cell membrane.

(D) Resistance to cephalosporins can be due to cleavage of the β-lactam ring.

The effects of endotoxin include each of the following EXCEPT:

(A) Opsonization

(B) Fever

(C) Activation of the coagulation cascade

(D) Hypotension

Bacterial surface structures that show antigenic diversity include each of the following EXCEPT:

(A) Pili

(B) Capsules

(C) Flagella

(D) Peptidoglycan

The effects of antibody on bacteria include each of the following EXCEPT:

(A) Lysis of gram-negative bacteria in conjunction with complement

(B) Augmentation of phagocytosis

(C) Increase in the frequency of lysogeny

(D) Inhibition of adherence of bacteria to mucosal surfaces

Each of the following statements concerning exotoxins is correct EXCEPT:

(A) When treated chemically, some exotoxins lose their toxicity and can be used as immunogens in vaccines.

(B) Some exotoxins are capable of causing disease in purified form, free of any bacteria.

(C) Some exotoxins act in the gastrointestinal tract to cause diarrhea.

(D) Some exotoxins contain lipopolysaccharides as the toxic component.

Each of the following statements concerning bacterial and human cells is correct EXCEPT:

(A) Bacteria are prokaryotic (i.e., they have one molecule of DNA, are haploid, and have no nuclear membrane), whereas human cells are eukaryotic (i.e., they have multiple chromosomes, are diploid, and have a nuclear membrane).

(B) Bacteria derive their energy by oxidative phosphorylation within mitochondria in a manner similar to human cells.

(C) Bacterial and human ribosomes are of different sizes and chemical compositions.

(D) Bacterial cells possess peptidoglycan, whereas human cells do not.

Each of the following statements concerning penicillin is correct EXCEPT:

(A) An intact β-lactam ring of penicillin is required for its activity.

(B) The structure of penicillin resembles that of a dipeptide of alanine, which is a component of peptidoglycan.

(C) Penicillin is a bacteriostatic drug because autolytic enzymes are not activated.

(D) Penicillin inhibits transpeptidases, which are required for cross-linking peptidoglycan.

Each of the following statements concerning the mechanisms of resistance to antimicrobial drugs is correct EXCEPT:

(A) R factors are plasmids that carry the genes for enzymes that modify one or more drugs.

(B) Resistance to some drugs is due to a chromosomal mutation that alters the receptor for the drug.

(C) Resistance to some drugs is due to transposon genes that code for enzymes that inactivate the drugs.

(D) Resistance genes are rarely transferred by conjugation.

Each of the following statements concerning endotoxins is correct EXCEPT:

(A) The toxicity of endotoxins is due to the lipid portion of the molecule.

(B) Endotoxins are found in most gram-positive bacteria.

(C) Endotoxins are located outside of the cell wall peptidoglycan.

(D) The antigenicity of somatic (O) antigen is due to repeating oligosaccharides.

Each of the following statements concerning exotoxins is correct EXCEPT:

(A) Exotoxins are polypeptides.

(B) Exotoxins are more easily inactivated by heat than are endotoxins.

(C) Exotoxins are less toxic than the same amount of endotoxins.

(D) Exotoxins can be converted to toxoids.

Each of the following statements concerning the killing of bacteria is correct EXCEPT:

(A) A 70% solution of ethanol kills more effectively than absolute (100%) ethanol.

(B) An autoclave uses steam under pressure to reach the killing temperature of 121°C.

(C) The pasteurization of milk kills pathogens but allows many organisms and spores to survive.

(D) Iodine kills by causing the formation of thymine dimers in bacterial DNA.

Each of the following statements concerning the drug depicted in the diagram is correct EXCEPT:

(A) The drug is bacteriostatic.

(B) The drug inhibits cell wall synthesis.

(C) The drug is made by a fungus.

(D) The portion of the molecule required for activity is labeled B.

Each of the following statements concerning the normal flora is correct EXCEPT:

(A) The normal flora of the colon consists predominantly of anaerobic bacteria.

(B) The presence of the normal flora prevents certain pathogens from colonizing the upper respiratory tract.

(C) Fungi (e.g., yeasts) are not members of the normal flora.

(D) Organisms of the normal flora are permanent residents of the body surfaces.

Each of the following statements concerning the structure and chemical composition of bacteria is correct EXCEPT:

(A) Some gram-positive cocci contain teichoic acid external to the peptidoglycan.

(B) Some gram-positive rods produce spores that are resistant to boiling.

(C) Some gram-negative rods contain lipid A in their outer cell membrane.

(D) Some mycoplasmas contain pentaglycine in their peptidoglycan.

Each of the following statements concerning the normal flora is correct EXCEPT:

(A) Streptococcus mutans is found in the mouth and contributes to the formation of dental caries.

(B) The predominant organisms in the alveoli are viridans streptococci.

(C) Bacteroides fragilis is found in greater numbers than Escherichia coli in the colon.

(D) Candida albicans is part of the normal flora of both men and women.

Each of the following statements concerning cholera toxin is correct EXCEPT:

(A) Cholera toxin inhibits elongation factor-2 in the mucosal epithelium.

(B) Binding of cholera toxin to the mucosal epithelium occurs via interaction of the B subunit of the toxin with a ganglioside in the cell membrane.

(C) Cholera toxin acts by adding ADP-ribose to a G protein.

(D) Cholera toxin activates the enzyme adenylate cyclase in the enterocyte.

Inhibit(s) bacterial RNA polymerase

(A) Penicillins

(B) Aminoglycosides

(C) Chloramphenicol

(D) Rifampin

(E) Sulfonamides

Inhibit(s) cross-linking of peptidoglycan

(A) Penicillins

(B) Aminoglycosides

(C) Chloramphenicol

(D) Rifampin

(E) Sulfonamides

Inhibit(s) protein synthesis by binding to the 30S ribosomal subunit

(A) Penicillins

(B) Aminoglycosides

(C) Chloramphenicol

(D) Rifampin

(E) Sulfonamides

Inhibit(s) folic acid synthesis

(A) Penicillins

(B) Aminoglycosides

(C) Chloramphenicol

(D) Rifampin

(E) Sulfonamides

During an outbreak of gastrointestinal disease caused by an Escherichia coli strain sensitive to ampicillin, tetracycline, and chloramphenicol, a stool sample from one patient yields E. coli with the same serotype resistant to the three antibiotics.

(A) Transduction

(B) Conjugation

(C) DNA transformation

(D) Transposition

A mutant cell line lacking a functional thymidine kinase gene was exposed to a preparation of DNA from normal cells; under appropriate growth conditions, a colony of cells was isolated that makes thymidine kinase.

(A) Transduction

(B) Conjugation

(C) DNA transformation

(D) Transposition

A retrovirus without an oncogene does not induce leukemia in mice; after repeated passages through mice, viruses recovered from a tumor were highly oncogenic and contained a new gene.

(A) Transduction

(B) Conjugation

(C) DNA transformation

(D) Transposition

Causes paralysis by blocking release of acetylcholine

(A) Diphtheria toxin

(B) Tetanus toxin

(C) Botulinum toxin