Quiz Answers
- 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 ß-hemolytic colonies on blood agar. For which one of the following sequelae is she MOST at risk?
- a. Bloody diarrhea
- b. Paralysis of the facial nerve (Bell’s palsy)
- c. Red blood cells and albumin in her urine ✅
- d. Blurred vision
- 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. Legionella pneumophila ✅
- b. Escherichia coli
- c. Enterococcus faecalis
- d. Klebsiella pneumoniae
- Acute glomerulonephritis is a nonsuppurative complication that follows infection by which one of the following organisms?
- a. Streptococcus pyogenes ✅
- b. Enterococcus faecalis
- c. Streptococcus agalactiae
- d. Streptococcus pneumoniae
- A 60-year-old woman is hospitalized following a stroke and develops a high-grade fever with chills. She is catheterized due to urinary incontinence and receives cephalosporin for treatment of pneumonia. Blood cultures and Gram stain are performed by the laboratory. The organisms isolated are gram-positive cocci that are catalase-negative and capable of growth in 6.5% sodium chloride. Which of the following is the most likely causal agent?
- a. Staphylococcus aureus
- b. Enterococcus faecalis ✅
- c. Viridans streptococci
- d. Streptococcus pyogenes
- e. Staphylococcus epidermidis
- A 27-year-old woman, after returning home from her honeymoon, has developed urinary frequency, dysuria, and urgency. Her urine is grossly bloody. Which lab data are most likely to define the causal agent?
- a. A gram-positive bacillus grown on a low oxidation-reduction medium
- b. An optochin-resistant, catalase-negative, gram-positive coccus
- c. A gram-negative diplococcus, which is oxidase positive but does not ferment maltose
- d. A gram-positive coccus, which is catalase positive and coagulase negative
- e. A gram-negative bacterium capable of reducing nitrates to nitrites ✅
- Four weeks after his arrival from Africa, a 24-year-old graduate student presents with blood in his urine. Microscopic examination of his urine reveals the presence of eggs with terminal spines. In the interview he admits that he has been working on his family’s rice field occasionally since his early childhood. The most likely etiologic agent of his complaint is
- a. Schistosoma haematobium ✅
- b. Schistosoma japonicum
- c. Entamoeba histolytica
- d. Schistosoma mansoni
- e. Fasciolopsis buski
- The first vaccine for human use produced using recombinant DNA technology was the:
- a. Hepatitis A vaccine
- b. Polio vaccine
- c. AIDS vaccine
- d. MMR vaccine
- e. Hepatitis B vaccine ✅
- Disease caused by which one of the following bacteria can be prevented by a toxoid vaccine?
- a. Haemophilus influenzae
- b. Streptococcus pneumoniae
- c. Corynebacterium diphtheriae ✅
- d. Salmonella typhi
- e. Neisseria meningitidis
- 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 induce a broader range of immune responses than do live, attenuated vaccines.
- c. Killed vaccines are safer to give to immunocompromised patients than are live, attenuated vaccines. ✅
- d. Killed vaccines are no longer used in this country because they do not induce secretory IgA.
- A 45-year-old man was attacked by a bobcat and bitten repeatedly about the face and neck. The animal was shot by a companion and brought back to the public health authorities. Once you decide to immunize against rabies virus, how would you proceed?
- a. Use hyperimmune serum and active immunization ✅
- b. Use active immunization only
- c. Use hyperimmune serum only
- A living microbe with reduced virulence that is used for vaccination is considered:
- a. Denatured
- b. Dormant
- c. Attenuated ✅
- d. A toxoid
- e. Virulent
- To design a vaccine against HIV infection, a logical goal would be to alter some native molecule or product of the virion in order to make it highly immunogenic. If you wished to prevent the attachment of the virus to helper T lymphocytes, which molecule or family of molecules might best be targeted?
- a. gp41
- b. p24
- c. nucleocapsid protein
- d. gp120 ✅
- e. p17
- Each of the following statements concerning rubella vaccine is correct EXCEPT:
- a. The immunogen in the vaccine is killed rubella virus. ✅
- b. The vaccine prevents reinfection, thereby limiting the spread of virulent virus.
- c. The incidence of both childhood rubella and congenital rubella syndrome has decreased significantly since the advent of the vaccine.
- d. The vaccine induces antibodies that prevent dissemination of the virus by neutralizing it during the viremic stage.
- 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. Immunization with tetanus toxoid induces effective protection against tetanus toxin. ✅
- c. The toxoid vaccine against Clostridium difficile infection should be administered to immunocompromised patients.
- d. Vaccines containing alpha toxin (lecithinase) are effective in protecting against gas gangrene.
- The MOST important protective function of the antibody stimulated by tetanus immunization is:
- a. To neutralize the toxin of the pathogen ✅
- b. To prevent adherence of the pathogen
- c. To prevent growth of the pathogen
- d. To opsonize the pathogen (Clostridium tetani)
- Each of the following statements concerning the rabies vaccine for use in humans is correct EXCEPT:
- a. If your patient is bitten by a wild animal (e.g., a skunk) the rabies vaccine should be given.
- b. The virus in the vaccine is grown in human cell cultures, thus decreasing the risk of allergic encephalomyelitis.
- c. When the vaccine is used for postexposure prophylaxis, rabies immune globulin should also be given.
- d. The vaccine contains live, attenuated rabies virus. ✅
- Each of the following parasites has an intermediate host as part of its life cycle EXCEPT:
- a. Echinococcus granulosus
- b. Taenia solium
- c. Trichomonas vaginalis ✅
- d. Toxoplasma gondii
- A 24-year-old primiparous woman in her eighth month of gestation develops a positive IgM titer to Toxoplasma gondii for the first time. She should be advised by her physician that
- a. future infections can be avoided by proper vaccination and worming of cats
- b. this child and all future fetuses are likely to be infected
- c. a newborn with a positive anti-Toxoplasma IgG response should be treated with anti-parasitics
- d. major organ damage can be reversed by prompt treatment of the newborn
- e. retinochoroiditis can be prevented by drug treatment of an infant with a positive IgM response ✅
- Which of the following statement(s) regarding Plasmodium falciparum are true?
- a. causes benign tertian malaria
- b. is the only malarial parasite causing greater than 20% parasitaemia ✅
- c. is associated with recurrent relapses after initial treatment because of liver hypnozoites
- d. is the only cause of cerebral malaria
- A 35-year-old man comes to the emergency department complaining of high fever, chills, severe headache, and confusion. He has recently returned from Africa. A peripheral blood smear reveals multiple ring structures and crescent-shaped gametes. Which of the following organisms is the most likely cause?
- a. Plasmodium ovale
- b. Leishmania species
- c. Plasmodium falciparum ✅
- d. Plasmodium malariae
- e. Plasmodium vivax
- After sporozoite gain entrance to human body it undergoes developmental cycle first in liver than in RBC, only after which fever is seen. This incubation period varies between plasmodium species, and ………….. species has longest incubation period.
- a. P. falciparum
- b. P. vivax
- c. P. ovale
- d. P. malariae ✅
- After one week vacationing in Mexico, a 14-year-old girl presents with abdominal pain, nausea, bloody diarrhea, and fever. Stool specimens are collected and sent to the laboratory for bacteriologic and parasitologic examination. Bacterial cultures are negative for intestinal pathogens. The laboratory report reveals organisms with red blood cells inside them. The most likely causal agent is
- a. Cryptosporidium parvum
- b. Giardia lamblia
- c. Shigella dysenteriae
- d. Entamoeba histolytica ✅
- e. Toxoplasma gondii
- Which one of the following protozoa primarily infects macrophages?
- a. Trypanosoma cruzi
- b. Leishmania donovani ✅
- c. Plasmodium vivax
- d. Trichomonas vaginalis
- Trophozoites, Schizonts and gametocytes of all the malarial parasites are seen in the peripheral blood smear except;
- a. P. falciparum ✅
- b. P. ovale
- c. P. vivax
- d. P. malariae
- How many pairs of flagella are present in the trophozoite of Giardia lamblia?
- a. Two pairs
- b. Three pairs
- c. Four pairs ✅
- d. One pair
- Each of the following statements concerning mucormycosis is correct EXCEPT:
- a. Hyphae typically invade blood vessels and cause necrosis of tissue.
- b. The fungi that cause mucormycosis are transmitted by airborne asexual spores.
- c. Ketoacidosis in diabetic patients is a predisposing factor to mucormycosis.
- d. Tissue sections from a patient with mucormycosis show budding yeasts. ✅
- Several fungi are associated with disease in immunocompromised patients. Which one of the following is the LEAST frequently associated?
- a. Mucor species
- b. Aspergillus fumigatus
- c. Malassezia furfur ✅
- d. Cryptococcus neoformans
- A 33-year-old HIV-positive man complains of headache and blurred vision. Physical examination reveals papilledema and ataxia. A head CT scan is normal, but CSF obtained by lumbar puncture reveals encapsulated organisms visible by India ink. Which of the following is true concerning this organism?
- a. It exists as a mycelial form at room temperature and a yeast at 37°C
- b. It is an encapsulated non-dimorphic yeast found worldwide ✅
- c. It consists of branching septate hyphae
- d. It is a nonencapsulated dimorphic yeast that reproduces by budding
- e. It can also be seen as “spaghetti and meatballs” on KOH stain
- You have made a clinical diagnosis of meningitis in a 50-year-old immunocompromised woman. A latex agglutination test on the spinal fluid for capsular polysaccharide antigen is positive. Of the following organisms, which one is the MOST likely cause?
- a. Candida albicans
- b. Aspergillus fumigatus
- c. Cryptococcus neoformans ✅
- d. Histoplasma capsulatum
- Each of the following statements concerning Candida albicans is correct EXCEPT:
- a. C. albicans causes thrush.
- b. C. albicans is transmitted primarily by respiratory aerosol. ✅
- c. Impaired cell-mediated immunity is an important predisposing factor to disease.
- d. C. albicans is a budding yeast that forms pseudohyphae when it invades tissue.
- You suspect that your patient’s disease may be caused by Cryptococcus neoformans. Which one of the following findings would be MOST useful in establishing the diagnosis?
- a. The finding of encapsulated budding cells in spinal fluid ✅
- b. A positive heterophil agglutination test for the presence of antigen
- c. Recovery of an acid-fast organism from the patient’s sputum
- d. A history of recent travel in the Mississippi River valley area
- A 55-year-old man who recently recovered uneventfully from a heart valve transplant presents to the emergency room with pleuritic chest pain, hemoptysis, fever, and chills. While he is being examined, he has a myocardial infarction and the medical team is unable to revive him. An autopsy revealed septate, acutely branching hyphae in many tissues. Which of the following organisms is most likely to be identified?
- a. Aspergillus fumigatus ✅
- b. Mucor species
- c. Histoplasma capsulatum
- d. Cryptococcus neoformans
- e. Blastomyces dermatitidis
- Your patient is a woman with a vaginal discharge. You suspect, on clinical grounds, that it may be due to Candida albicans. Which one of the following statements is LEAST accurate or appropriate?
- a. The clinical laboratory can use germ tube formation to identify the isolate as C. albicans.
- b. Antibiotics predispose to Candida vaginitis by killing the normal flora lactobacilli that keep the vaginal pH low.
- c. Culture of the discharge on Sabouraud’s agar should produce a white mycelium with aerial conidia. ✅
- d. A Gram stain of the discharge should reveal budding yeasts.
- Aspergillus fumigatus can be involved in a variety of clinical conditions. Which one of the following is LEAST likely to occur?
- a. Allergy following inhalation of airborne particles of the fungus
- b. Colonization of tuberculous cavities in the lung
- c. Tissue invasion in immunocompromised host
- d. Thrush ✅
- A 42-year-old man who has AIDS presents to his physician with progressively increasing dyspnea over the past 3 weeks. He also complains of a dry, painful cough, fatigue, and low-grade fever. A chest x-ray reveals bilateral symmetrical interstitial and alveolar infiltration. Which of the following agents is the most likely cause of the above?
- a. Toxoplasma gondii
- b. Histoplasma capsulatum
- c. Pneumocystis jiroveci ✅
- d. Cryptococcus neoformans
- e. Cryptosporidium parvum
- A 15-year-old member of the high school swim team notices painless, umbilicated cutaneous lesions on the toes. Large eosinophilic cytoplasmic inclusions are present in the affected epithelia. What is the most likely causal agent?
- a. Adenovirus
- b. Herpes simplex virus
- c. Human papilloma virus
- d. Molluscum contagiosum virus ✅
- Nagler’s reaction is useful for the identification of
- a. Clostridium botulinum
- b. Clostridium perfringens ✅
- c. Clostridium tetani
- d. Clostridium difficile
- A 35-year-old man who is positive for HIV develops sepsis with the subsequent development of a necrotic lesion on the buttock that has a black center and an erythematous margin. Which of the following is the most likely causal agent?
- a. Enterococcus faecalis ✅
- b. Pseudomonas aeruginosa
- c. Bacillus anthracis
- d. Clostridium perfringens
- Each of the following statements concerning Clostridium perfringens is correct EXCEPT:
- a. It causes gas gangrene.
- b. It produces an exotoxin that degrades lecithin and causes necrosis and hemolysis.
- c. It is a gram-negative rod that does not ferment lactose. ✅
- d. It causes food poisoning.
- 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 ß-hemolytic colonies on blood agar. For which one of the following sequelae is she MOST at risk?
- a. Blurred vision
- b. Bloody diarrhea
- c. Red blood cells and albumin in her urine ✅
- d. Paralysis of the facial nerve (Bell’s palsy)
- Each of the following statements concerning clostridia is correct EXCEPT:
- a. Anaerobic conditions at the wound site are not required to cause tetanus, because spores will form in the presence of oxygen. ✅
- b. Pathogenic clostridia are found both in the soil and in the normal flora of the colon.
- c. Botulism, which is caused by ingesting preformed toxin, can be prevented by boiling food prior to eating.
- d. Antibiotic-associated (pseudomembranous) colitis is due to a toxin produced by Clostridium difficile.
- Contamination of umbilical cord at birth may lead to infection by:
- a. Clostridium difficile
- b. Clostridium perfringens
- c. Clostridium botulinum
- d. Clostridium tetani ✅
- Stormy clot reaction is useful in the identification of:
- a. Clostridium tetani
- b. Clostridium perfringens ✅
- c. Clostridium difficile
- d. Clostridium botulinum
- Each of the following statements concerning Staphylococcus aureus is correct EXCEPT:
- a. The coagulase test is positive.
- b. Endotoxin is an important pathogenetic factor. ✅
- c. Treatment should include a ß-lactamase–resistant penicillin.
- d. Gram-positive cocci in grapelike clusters are seen on Gram-stained smear.
- A 25-year-old man gets into a fight at the local bar and punches another patron in the mouth. The following day his fist becomes infected and he visits a local urgent care center. Exudate from the wound is cultured on blood and chocolate agar and reveals gram-negative rods that have a bleach-like odor. Which of the following agents is the most likely cause?
- a. Actinobacillus actinomycetemcomitans
- b. Pseudomonas aeruginosa
- c. Eikenella corrodens ✅
- d. Kingella kingae
- e. Cardiobacterium hominis
- 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. Fusobacterium nucleatum and Peptostreptococcus intermedius
- b. Clostridium perfringens and Chlamydia psittaci
- c. Listeria monocytogenes and Legionella pneumophila
- d. Nocardia asteroides and Mycoplasma pneumoniae ✅
- Which one of the following organisms is MOST likely to be the cause of pneumonia in an immunocompetent young adult?
- a. Nocardia asteroides
- b. Mycoplasma pneumoniae ✅
- c. Serratia marcescens
- d. Legionella pneumophila
- Each of the following statements concerning Corynebacterium diphtheriae is correct EXCEPT:
- a. Toxin production is dependent on the organism’s being lysogenized by a bacteriophage.
- b. Antitoxin should be used to treat patients with diphtheria.
- c. Diphtheria toxoid should not be given to children younger than 3 years because the incidence of complications is too high. ✅
- d. C. diphtheriae is a gram-positive rod that does not form spores.
- 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 tetanus toxoid
- c. The vaccine containing killed Bordetella pertussis ✅
- d. The vaccine containing diphtheria toxoid
- Each of the following statements concerning certain gram-negative rods is correct EXCEPT:
- a. Legionella pneumophila infection is acquired by inhalation of aerosols from environmental water sources.
- b. Whooping cough, which is caused by Bordetella pertussis, is on the rise because changing antigenicity of the organism has made the vaccine relatively ineffective. ✅
- c. In unimmunized individuals, invasive disease caused by Haemophilus influenzae is most often due to strains possessing a type b polysaccharide capsule.
- d. Pseudomonas aeruginosa causes wound infections that are characterized by blue-green pus as a result of pyocyanin production.
