A 4-year-old girl has papular and pustular lesions on her face. The lesions are exuding a honey-colored serous fluid. You make a clinical diagnosis of impetigo. A Gram stain of the exudate reveals gram-positive cocci in chains, and a culture reveals β-hemolytic colonies on blood agar. For which one of the following sequelae is she MOST at risk?
(C) Paralysis of the facial nerve (Bell’s palsy)
(D) Red blood cells and albumin in her urine
The purified genome of certain RNA viruses can enter a cell and elicit the production of progeny viruses (i.e., the genome is infectious). Regarding these viruses, which one of the following statements is MOST accurate?
(A) They have a segmented genome.
(B) They have a polymerase in the virion.
(C) Their genome RNA is double-stranded.
(D) They encode a protease that cleaves a precursor polypeptide.
(E) Their genome RNA has the same base sequence as mRNA.
A 77-year-old man with enterococcal endocarditis needed to be treated with penicillin G but had a history of a severe penicillin reaction. He was therefore skin tested using penicilloyl-polylysine as the antigen. Which one of the following is MOST likely to occur in a positive skin test?
(A) The antigen forms immune complexes with IgG.
(B) The antigen activates CD4-positive T cells and macrophages.
(C) The antigen activates the alternative pathway of complement.
(D) The antigen activates CD8-positive T cells by binding to class I MHC proteins.
(E) The antigen cross-links IgE on the mast cells and causes the release of histamine.
Regarding the Gram stain, which one of the following is the MOST accurate?
(A) After adding crystal violet and Gram’s iodine, both gram-positive bacteria and gram-negative bacteria will appear blue.
(B) If you forget to stain with the red dye (safranin or basic fuchsin), both gram-positive bacteria and gram-negative bacteria will appear blue.
(C) If you forget to heat-fix, both gram-positive bacteria and gram-negative bacteria will appear blue.
(D) One reason why bacteria have a different color in this stain is because the gram-positive bacteria have lipid in their membrane, whereas gram-negative bacteria do not.
A 35-year-old man with a CD4 count of 50 presents with a skin nodule on his chest. The nodule is about 3 cm in diameter and is not red, hot, or tender. He says it has been slowly growing bigger for the past 3 weeks. You biopsy the nodule, and the pathologist calls to say that the patient has disseminated cryptococcosis. Which one of the following is the BEST description of what the pathologist saw in the biopsy specimen?
(D) Budding yeasts with a thick capsule
(E) Septate hyphae with low-angle branching
A 22-year-old woman complains of a persistent nonproductive cough and a fever of 101°F that came on slowly over the last 4 days. Physical examination reveals some rales in the left lung base. A patchy infiltrate is seen on chest X-ray. She works as a secretary in a law office and has not traveled recently. She is not immunocompromised and has not been hospitalized recently. A sample of her serum agglutinates red blood cells at 4°C but not at 37°C. Which one of the following BEST describes the organism that is the MOST likely cause of her disease?
(A) A very small bacterium that has no cell wall
(B) A gram-negative diplococcus with a large capsule
(C) An acid-fast rod that forms colonies within 7 days
(D) A filamentous gram-positive rod that is weakly acid-fast
(E) A spirochete that has never been grown on blood agar
The mother of a 4-year-old child notes that her child is sleeping poorly and scratching his anal area. You suspect the child may have pinworms. Which one of the following is the BEST method to make that diagnosis?
(A) Examine the stool for the presence of cysts
(B) Examine the stool for the presence of trophozoites
(C) Examine a blood smear for the presence of microfilaria
(D) Determine the titer of IgE antibody against the organism
(E) Examine transparent adhesive tape for the presence of eggs
Regarding bacterial spores, which one of the following is the MOST accurate?
(A) One spore germinates to form one bacterium.
(B) They are produced primarily within human red blood cells.
(C) They are killed by boiling at sea level but not at high altitude.
(D) They are produced by anaerobes only in the presence of oxygen.
(E) They contain endotoxin, which accounts for their ability to cause disease.
A 22-year-old woman had fever to 100°F and anorexia for the past 2 days, and this morning she appears jaundiced. On examination, her liver is enlarged and tender. She has a total bilirubin of 5 mg/dL (normal, <1) and elevated transaminases. She received the complete course of the hepatitis B vaccine 2 years ago but has not had the hepatitis A vaccine. The results of her hepatitis serologies are as follows: HAV-IgM negative, HAV-IgG positive, HBsAg negative, HBsAb positive, HBcAb negative, HCV-Ab positive. Of the following, which one is the MOST accurate?
(A) She probably has hepatitis A now, probably has not been infected with hepatitis B virus (HBV), and probably had hepatitis C in the past.
(B) She probably has hepatitis A now, probably has been infected with HBV in the past, and probably had hepatitis C in the past.
(C) She has been infected with hepatitis A virus (HAV) in the past, probably has not been infected with HBV, and probably has hepatitis C now.
(D) She has been infected with HAV in the past, probably has hepatitis B now, and probably had hepatitis C in the past.
Regarding the function of the different classes of antibodies, which one of the following statements is the MOST accurate?
(A) IgA acts as an antigen receptor on the surface of B cells.
(B) IgG activates the alternative pathway of complement, resulting in the production of C3a that degrades the bacterial cell wall.
(C) IgG binds to the bacterial surface and makes the bacteria more easily ingested by phagocytes.
(D) IgM defends against worm parasites, such as hookworms.
(E) IgE blocks the binding of viruses to the gut mucosa.
A 6-year-old boy fell and sustained a deep wound from a rusty nail that penetrated his thigh. His mother removed the nail and cleaned the wound with soap and water. The next morning, he had a temperature of 102°F, and his thigh was very painful and swollen. In the emergency room, crepitus (gas in the tissue) was noted. A Gram stain of exudate from the wound area revealed large gram-positive rods. Which one of the following is the MOST likely cause?
(B) Clostridium perfringens
(D) Listeria monocytogenes
(E) Mycobacterium fortuitum-chelonei complex
(G) Pseudomonas aeruginosa
The two most common types of viral vaccines are killed vaccines and live, attenuated vaccines. Regarding these vaccines, which one of the following statements is the MOST accurate?
(A) Killed vaccines induce a longer-lasting response than do live, attenuated vaccines.
(B) Killed vaccines are no longer used in this country because they do not induce secretory IgA.
(C) Killed vaccines induce a broader range of immune responses than do live, attenuated vaccines.
(D) Killed vaccines are safer to give to immunocompromised patients than are live, attenuated vaccines.
Regarding immediate (type I) and immune complex (type III) hypersensitivities, which one of the following is the MOST accurate?
(A) IgE is involved in both immediate and immune complex hypersensitivities.
(B) Complement is involved in both immediate and immune complex hypersensitivities.
(C) Less antigen is typically needed to trigger an immediate reaction than an immune complex reaction.
(D) Neutrophils play a more important role in immediate reactions than in immune complex reactions.
Disease caused by which one of the following bacteria can be prevented by a toxoid vaccine?
(D) Corynebacterium diphtheriae
(E) Haemophilus influenzae
(F) Listeria monocytogenes
(G) Neisseria meningitidis
(I) Streptococcus pneumoniae
A 50-year-old woman has had a gradual onset of headaches that have become increasingly more severe during the past 3 weeks. On examination, she is confused regarding time, place, and person, and she is febrile to 39°C. Her spinal fluid reveals a normal glucose, normal protein, and 17 cells, all of which were lymphocytes. Gram stain of the spinal fluid shows no organism. An MRI reveals a 2-cm radiolucent lesion in the temporal lobe. A biopsy of the brain lesion was performed. A Giemsa stain of the tissue shows multinucleated giant cells with intranuclear inclusion bodies. Which one of the following is the MOST likely causative organism?
(D) Herpes simplex virus type 1
An 80-year-old man had a carcinoma of the colon removed 3 days ago. He was doing well until this morning, when he spiked a fever to 39°C and complained of severe abdominal pain. Examination revealed a “board-like” abdomen indicative of peritonitis. He was taken to the operating room, where it was discovered that his anastomosis had broken down and bowel contents had spilled into the peritoneal cavity. A foul-smelling exudate was observed. A Gram stain of the peritoneal exudate revealed many gram-negative rods. Which one of the following sets of bacteria is the MOST likely cause of this infection?
(A) Escherichia coli and Brucella melitensis
(B) Enterobacter cloacae and Salmonella enteritidis
(C) Fusobacterium nucleatum and Bacteroides fragilis
(D) Haemophilus influenzae and Actinomyces israelii
(E) Shigella dysenteriae and Serratia marcescens
Regarding the primary and secondary antibody responses, which one of the following statements is MOST accurate?
(A) The IgM made in the primary response is made primarily by memory B cells.
(B) The lag phase is shorter in the response than in the secondary response.
(C) In the primary response, memory B cells are produced, but memory T cells are not.
(D) Antigen must be processed and presented in the primary response but not in the secondary response.
(E) The amount of IgG made in the secondary response is greater than the amount made in the primary response.
A 70-year-old man who is receiving chemotherapy for leukemia develops a fever to 40°C and has two episodes of teeth-chattering chills, and his blood pressure drops to 80/20 mmHg. Of the following factors, which one is MOST likely to be the cause of his fever, chills, and hypotension?
(G) Polysaccharide capsule
A 22-year-old woman presents with “the worst sore throat I’ve ever had.” She also complains of fatigue and anorexia. She is not immunocompromised and has not been hospitalized recently. On examination, she is febrile to 38°C, the pharynx is inflamed, and there are a few tender cervical nodes bilaterally. There are no white lesions on the tongue or pharynx. A throat culture grows α-hemolytic colonies on blood agar that are optochin-resistant. Of the following, which one is the MOST likely cause?
(H) Streptococcus pneumoniae
(I) Streptococcus pyogenes
(J) Strongyloides stercoralis
Regarding the complement pathway, which one of the following is MOST accurate?
(A) C5a mediates chemotaxis and attracts neutrophils to the site of infection.
(B) C5b plays an important role in the opsonization of gram-negative bacteria.
(C) C3a is a decay-accelerating factor that causes the rapid decay and death of bacteria.
(D) C1 binds to the surface of gram-positive bacteria, which initiates the classic pathway.
(E) The membrane attack complex is produced in the classic pathway but not in the alternative pathway.
A 65-year-old woman had symptoms of dementia. An MRI revealed significant cortical atrophy. It was determined that her intraventricular pressure was very high, and a ventriculoperitoneal shunt (from the brain, tunneling under the skin into the peritoneal cavity) was placed to relieve the pressure. Three weeks later, she developed a fever to 38°C, malaise, and anorexia but no other symptoms. Of the following, which one BEST describes the MOST likely organism causing her current symptoms?
(A) A gram-positive coccus that does not clot plasma
(B) A curved gram-negative rod that produces urease
(C) An acid-fast rod that does not grow on bacteriologic media
(D) An obligate intracellular parasite that forms a cytoplasmic inclusion body
(E) A spirochete that induces an antibody that agglutinates a lipid from a cow’s heart
Two mutants of poliovirus, one mutated at gene X and the other mutated at gene Y, have been isolated. If a cell is infected with each mutant alone, no virus is produced. If a cell is infected with both mutants, which one of the following is MOST likely to occur?
(A) Complementation between the mutant gene products may occur, and, if so, both X and Y progeny viruses will be made.
(B) Phenotypic mixing may occur, and, if so, both X and Y progeny viruses will be made.
(C) Reassortment of the genome segments may occur, and, if so, both X and Y progeny viruses will be made.
(D) The genome may be transcribed into DNA, and, if so, both X and Y viruses will be made.
A 40-year-old woman has a history of chronic inflammation of the small joints of the hands bilaterally. You suspect rheumatoid arthritis. Which one of the following statements is the MOST accurate regarding the pathogenesis of this disease?
(A) It is caused by sensitized CD4-positive T lymphocytes and macrophages invading the joints.
(B) It is caused by antibody against human IgG-forming immune complexes within the joints.
(C) It is caused by the release of mediators from mast cells when environmental agents cross-link adjacent IgEs within the joints.
(D) It is caused by superantigens inducing the release of large amounts of lymphokines from helper T cells within the joints.
Listed below are five bacteria paired with a mode of transmission. Which one of the pairings is MOST accurate?
(A) Borrelia burgdorferi—mosquito bite
(B) Coxiella burnetii—bat guano
(C) Haemophilus influenzae—penetrating wound contaminated with soil
(D) Rickettsia rickettsii—contaminated food
(E) Yersinia pestis—flea bite
A 70-year-old man with leukemia initially responded to chemotherapy but now is refractory. He therefore underwent a bone marrow transplant and is now receiving large doses of cyclosporine A and prednisone. Three weeks after the transplant, he became febrile to 39°C and began coughing up purulent sputum. A chest X-ray revealed pneumonia. A Gram stain of the sputum did not reveal a predominant organism, but a KOH prep of the sputum revealed septate hyphae with parallel walls and low-angle branching. Of the following organisms, which one is MOST likely to be the cause of this pneumonia?
(A) Aspergillus fumigatus
(D) Cryptococcus neoformans
Your patient is a 20-year-old woman with severe diarrhea that began yesterday. She has just returned from a 3-week trip to Peru, where she ate some raw shellfish at the farewell party. She now has 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. Of the following organisms, which one is MOST likely to be the cause of her diarrhea?
(C) Entamoeba histolytica
(G) Yersinia enterocolitica
A 50-year-old man has had low-grade, persistent headaches for several months. In the past few days, nausea, vomiting, and blurred vision have occurred. An MRI reveals several cystlike lesions in the brain parenchyma. The patient lived for many years on one of the small Caribbean islands. On the basis of a positive serologic test, a diagnosis of neurocysticercosis was made. Which one of the following is the MOST likely mode by which this disease was acquired?
(D) Ingestion of the larvae of the organism in raw fish
(E) Ingestion of the eggs of the organism in contaminated food
(F) Penetration of the skin by the organism while walking bare-footed
(G) Penetration of the skin by the organism while bathing in fresh water
A 30-year-old woman with a previous history of rheumatic fever now has a fever for the past 2 weeks. Physical examination reveals a new heart murmur. You suspect endocarditis and do a blood culture, which grows a viridans group Streptococcus later identified as Streptococcus sanguinis. Of the following body sites, which one is the MOST likely source of this organism?
Regarding poliovirus, which one of the following is MOST accurate?
(A) Poliovirus remains latent within sensory ganglia, and reactivation occurs primarily in immunocompromised patients.
(B) When the live, attenuated virus in the oral vaccine replicates, revertant mutants can occur that can cause paralytic polio.
(C) The widespread use of the killed vaccine in the countries of North and South America has led to the virtual elimination of paralytic polio in those areas.
(D) The current recommendation is to give the live, attenuated vaccine for the first three immunizations to prevent the child from acting as a reservoir, followed by boosters using the killed vaccine.
Regarding ABO and Rh blood types, which one of the following is the MOST accurate?
(A) People with type O are called universal recipients because they have antibodies against H substance but not against A and B antigens.
(B) If the father is Rh-positive and the mother is Rh-negative, hemolytic disease of the newborn only occurs when the child is Rh-negative.
(C) People who are Rh-negative usually have antibodies to the Rh antigen because they are exposed to cross-reacting antigen located on bacteria in the colon.
(D) If type A blood is transfused into a person with type B blood, complement will be activated, and the membrane attack complex will cause lysis of the type A red cells.
A 25-year-old man was in a motorcycle accident 3 days ago, in which he sustained severe head trauma. He has had spinal fluid leaking from his nose since the accident and now develops a severe headache. His temperature is 39°C, and on examination, you find nuchal rigidity. You do a lumbar puncture and find that the spinal fluid is cloudy and contains 5000 WBC/mL, 90% of which are polys. Of the following, which one is the MOST likely result observed in the laboratory analysis of the spinal fluid?
(A) Gram-negative rods that grew only on Thayer-Martin medium
(B) A motile spirochete that formed beta-hemolytic colonies on blood agar
(C) Gram-positive cocci that formed alpha-hemolytic colonies on blood agar
(D) Gram-positive rods that grew only on chocolate agar supplemented with X and V factors
(E) No organism was seen using Gram stain, but tissue stains revealed cytoplasmic inclusion bodies
Regarding prions and prion-caused diseases, which one of the following is MOST accurate?
(A) Prions are highly resistant to both ultraviolet light and to boiling but are inactivated by hypochlorite.
(B) Prions are protein-containing particles surrounded by a lipoprotein envelope with a DNA polymerase in the envelope.
(C) The diagnosis of prion-caused diseases such as Creutzfeldt-Jakob disease is typically made by observing cytopathic effect in cell culture.
(D) Creutzfeldt-Jakob disease occurs primarily in children younger than the age of 2 years because they cannot mount an adequate immune response to the prion protein.
A 2-year-old boy has had several infections of the sinuses and lungs and is being evaluated to determine whether he has chronic granulomatous disease. Regarding this disease, which one of the following is the MOST accurate?
(A) There is a deficiency in NADPH oxidase activity.
(B) The defect is primarily in antigen-presenting cells such as macrophages.
(C) Pneumocystis jiroveci infections are common in patients with this disease.
(D) The diagnosis is primarily made by ELISA, in which antibody against the affected cell component is detected.
Regarding Chlamydiae, which one of the following is MOST accurate?
(A) They are gram-positive rods that do not form spores.
(B) They exhibit swarming motility on a blood agar plate.
(C) Their life cycle consists of a metabolically inactive particle in the extracellular phase.
(D) They can replicate only within cells because they lack the ability to produce certain essential mRNAs.
(E) They replicate in the nucleus of infected cells, where they form inclusions that are useful diagnostically.
Regarding human papillomavirus (HPV), which one of the following is MOST accurate?
(A) Blood and blood products are an important mode of transmission of HPV.
(B) HPV is an enveloped virus with a genome composed of double-stranded RNA.
(C) Amantadine is a chain-terminating drug that inhibits HPV replication by blocking DNA synthesis.
(D) HPV induces the formation of koilocytes in the skin that are an important diagnostic feature of HPV infection.
(E) The P2 capsid protein of HPV activates the c-sarc oncogene in human cells, which is the process by which HPV predisposes to malignancy.
Regarding Lyme disease, which one of the following is MOST accurate?
(A) The causative organism is a small gram-positive rod.
(B) Mice are the main reservoir of the causative organism.
(C) The Lyme disease vaccine contains toxoid as the immunogen.
(D) Fleas are the principal mode of transmission of the causative organism.
(E) The diagnosis in the clinical laboratory is typically made by culturing the organism on chocolate agar.
Regarding Bruton’s agammaglobulinemia, which one of the following is the MOST accurate?
(A) VDJ gene switching does not occur.
(B) There is very little IgG, but IgM and IgA levels are normal.
(C) The number of B cells is normal, but they cannot differentiate into plasma cells.
(D) There is a defect in a tyrosine kinase, one of the enzymes in the signal transduction pathway.
(E) Viral infections are more common in patients with this disease than are pyogenic bacterial infections.
A 20-year-old woman presents with a history of vaginal discharge for the past 3 days. On pelvic examination, you see a mucopurulent exudate at the cervical os, and there is tenderness on palpation of the right fallopian tube. You do a Gram stain and culture on the cervical discharge. The culture is done on Thayer-Martin medium, which is a chocolate agar that contains antibiotics that inhibit the growth of normal flora. Of the following, which findings are the MOST likely to be found?
(A) A Gram stain reveals many neutrophils and spirochetes, and culture on Thayer-Martin medium reveals no colonies.
(B) A Gram stain reveals many neutrophils and gram-variable rods, and culture on Thayer-Martin medium reveals β-hemolytic colonies.
(C) A Gram stain reveals many neutrophils and gram-negative diplococci, and culture on Thayer-Martin medium reveals oxidase-positive colonies.
(D) A Gram stain reveals many neutrophils but no gram-negative diplococci are seen, and culture on Thayer-Martin medium reveals coagulase-positive colonies.
Regarding human immunodeficiency virus (HIV), which one of the following is MOST accurate?
(A) The term viral load refers to the concentration of HIV RNA in the patient’s blood.
(B) Both zidovudine and lamivudine block HIV replication by inhibiting cleavage of the precursor polypeptide by the virion-encoded protease.
(C) The antigenicity of the GAG protein of HIV is highly variable, which is a significant impediment to the development of a vaccine against HIV.
(D) Highly active antiretroviral therapy (HAART) consists of a “backbone” of zidovudine and lamivudine plus either enfuvirtide or maraviroc.
Regarding Th-1 and Th-2 cells, which one of the following is MOST accurate?
(A) Th-1 cells produce gamma interferon and promote cell-mediated immunity.
(B) Th-2 cells produce interleukin-17, which inhibits the formation of Th-1 cells.
(C) Both Th-1 and Th-2 cells have class II MHC proteins on their outer cell membrane.
(D) Before they differentiate into Th-1 or Th-2 cells, naïve Th cells are double-positives (i.e., they produce both gamma interferon and interleukin-4).