USMLE Microbiology Exam Practice Test

146 Questions | Total Attempts: 97

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Microbiology Quizzes & Trivia

Questions and Answers
  • 1. 
    A 5-year-old child who recently moved from Eastern Europe is brought to the emergency room with difficulty breathing and a low-grade fever. Physical examination reveals a grayish pharyngeal exudate, enlarged cervical lymph nodes and partial soft palate paralysis. Bacteria isolated from the pharyngeal exudate demonstrate exotoxin production in the laboratory. This exotoxin acts via the following mechanism:
    • A. 

      Intracellular protein ribosylation

    • B. 

      Degradation of lecithin

    • C. 

      Increased sensitivity to histamine

    • D. 

      Inactivation of the 60s ribosomal subunit

    • E. 

      Autoimmune activation by antigenic mimicry

  • 2. 
    An 8-year-old Caucasian boy is brought to your office with throat pain, fever and malaise. Physical examination reveals white exudates on his tonsils and swollen anterior cervical lymph nodes. If the boy returns in a month with fatigue, joint pain and chest pain and later in life he develops a heart murmur, which of the following would be the most likely explanation for his condition?
    • A. 

      Protein A-mediated opsonization block

    • B. 

      Bacterial and human epitope homology

    • C. 

      Immune complex deposition

    • D. 

      Exotoxin-induced T-cell receptor activation

    • E. 

      Coronary artery aneurysm formation

  • 3. 
    A 67-year-old male is hospitalized with low-grade fevers, fatigue and a diastolic murmur at the left sternal border. Blood cultures reveal Gram positive cocci that are catalase-negative and able to grow in 6.5% saline. This patient's medical history is most likely to reveal which of the following procedures in the past month?
    • A. 

      Dental extraction

    • B. 

      Skin biopsy

    • C. 

      Sinus drainage

    • D. 

      Nasal polypectomy

    • E. 

      Cystoscopy

  • 4. 
    Infective endocarditis is known to be caused by many different bacterial species. Which of the following scenarios is most consistent with infective endocarditis caused by Streptococcus bovis?
    • A. 

      A 34-year-old female with known mitral stenosis develops low-grade fevers and negative blood cultures

    • B. 

      A 45-year-old male complains of fatigue and exertional dyspnea three weeks after tooth extraction

    • C. 

      A 62-year-old female has a persistent fever after being diagnosed with colon cancer

    • D. 

      A 64-year-old male with repeatedly negative blood cultures has small mitral vegetation on transesophageal echocardiogram

    • E. 

      A 29-year-old male with a persistent fever has tricuspid vegetations and tricuspid regurgitation on transthoracic echocardiogram

  • 5. 
    Gram-positive cocci isolated from the blood of a patient with bacteremia synthesize dextrans from glucose. The bacteria most likely contribute to which of the following pathological states?
    • A. 

      Glomerulonephritis

    • B. 

      Sarcoidosis

    • C. 

      Erythema nodosum

    • D. 

      Migratory polyarthritis

    • E. 

      Anterior uveitis

    • F. 

      Dental caries

  • 6. 
    Transient bacteremia is demonstrated in a healthy 22-year-old male after a dental procedure. The Gram-positive bacteria isolated from the blood synthesize dextrans from sucrose. Which of the following would be the most likely adherence site for these bacteria?
    • A. 

      Endothelial surface glycoproteins

    • B. 

      Subendothelial collagen

    • C. 

      Subendothelial glycosaminoglycans

    • D. 

      Circulating heparins

    • E. 

      Fibrin-platelet aggregates

  • 7. 
    A group of physicians in a developing country is advocating the early empiric use of penicillin in the treatment of clinically diagnosed bacterial pharyngitis, a condition that is quite common in children of that nation. What would you expect to decrease as a result of their policy in the long term?
    • A. 

      Expensive antibiotic requirement

    • B. 

      Nephritic disease

    • C. 

      Deaths caused by diarrhea

    • D. 

      Bronchial asthma hospitalizations

    • E. 

      Cardiac surgeries

    • F. 

      Vaccination needs

  • 8. 
    A 62-year-old Caucasian male who recently underwent a mitral valve replacement is having low-grade fevers. He also complains of dyspnea and malaise. Repeated blood cultures grow Gram-positive cocci in clusters that are catalase-positive and coagulase-negative. Which of the following is the best initial treatment for this patient?
    • A. 

      Penicillin G

    • B. 

      Nafcillin

    • C. 

      Vancomycin

    • D. 

      Ciprofloxacin

    • E. 

      Erythromycin

    • F. 

      Ceftriaxone

  • 9. 
    A 52-year-old male is having low-grade fevers after recent replacement of his aortic valve. Repeated blood cultures grow gram-positive cocci. Which of the following characteristics is most consistent with Staphylococcus epidermidis as the cause of this patient's symptoms?
    • A. 

      Catalase negative

    • B. 

      Coagulase negative

    • C. 

      Mannitol fermenting

    • D. 

      Novobiocin resistance

    • E. 

      Yellow pigment production

  • 10. 
    An 8-year-old male who recently moved to the United States from Asia is brought to the emergency room with throat pain and difficulty breathing. Soon after being admitted to the hospital, he dies of severe heart failure. In the laboratory, bacterial isolates from this patient's tonsils are found to cause rapid death of 8 out of 1 O exposed guinea pigs. Two of the 10 experimental animals survive. The surviving animals most likely possess which of the following antibodies?
    • A. 

      LgA against adhesion proteins

    • B. 

      Opsonizing lgM

    • C. 

      Complement-fixing lgM

    • D. 

      Immobilizing lgG

    • E. 

      LgG against circulating proteins

  • 11. 
    A 29-year-old female presents to clinic with malaise and an extremely painful rash in her genital region. She has never had such symptoms before. Tzanck smear of the genital lesion is positive for multinucleated giant cells. A drug that can cause rapid resolution of this patient's symptoms would most likely:
    • A. 

      Prevent viral attachment to target cells

    • B. 

      Inhibit viral protease activity

    • C. 

      Incorporate into newly replicated viral DNA

    • D. 

      Prevent virion release from infected cells

    • E. 

      Up-regulate interferon synthesis in infected cells

  • 12. 
    A 17-year-old female presents to your office with dark urine and facial puffiness. She had a minor skin infection several weeks ago that resolved spontaneously. Microscopic examination of the urine sediment shows red blood cell casts. The organism responsible for this patient's symptoms would most likely demonstrate:
    • A. 

      Catalase positivity

    • B. 

      Growth in 6.5% NaCl

    • C. 

      Bile solubility

    • D. 

      Bacitracin sensitivity

    • E. 

      Optochin sensitivity

  • 13. 
    A 23-year-old Caucasian female presents to clinic with lower abdominal pain and scant bloody vaginal discharge. She has been sexually active with multiple partners and uses condoms on occasion. She has been treated for "genital infections" in the past but denies any history of pregnancy. Her blood pressure is 11 2/70 mm Hg while supine and 96/60 mm Hg while standing. A pregnancy test is positive. Which of the following microorganisms is most likely responsible for this patient's current condition?
    • A. 

      Gardnerella vaginalis

    • B. 

      Neisseria gonorrhoeae

    • C. 

      Trichomonas vaginalis

    • D. 

      Treponema pallidum

    • E. 

      Herpes simplex virus

    • F. 

      Molluscum contagiosum

  • 14. 
    A group of investigators is trying to develop an anti-gonococcal vaccine. Their attempts to use pilus components to induce long-lasting immunity would most likely fail because of:
    • A. 

      Antigenic mimicry

    • B. 

      Low molecular weight

    • C. 

      Non-protein structure

    • D. 

      Antigenic variation

    • E. 

      Local immunosuppression

  • 15. 
    A 26-year-old male presents to your office with dysuria and urethral discharge two weeks after having unprotected sexual intercourse with a new partner. Gram stain of the discharge reveals numerous neutrophils with intracellular diplococci. A sample of the discharge is placed on an antibiotic-containing medium, and bacterial colonies are cultured. This medium is best described as:
    • A. 

      Enrichment

    • B. 

      Differential

    • C. 

      Synthetic

    • D. 

      Selective

    • E. 

      Reducing

  • 16. 
    A 7-year-old Caucasian boy is brought to your office with blisters on his face. Some of the blisters have broken and are covered with golden yellow crusts. Exudate microscopy reveals Gram-positive cocci in chains. Which of the following would be a component of the clinical syndrome that may follow such an infection?
    • A. 

      Joint pain and eye redness

    • B. 

      Fatigue and heart murmurs

    • C. 

      Face puffiness and dark urine

    • D. 

      Bilateral facial nerve palsy

    • E. 

      Abdominal pain and jaundice

  • 17. 
    A 34-year-old woman comes to the physician because of itching around her vulva and vaginal discharge. She has no other complaints. Her other medical problems include chronic allergic rhinitis, for which she takes intranasal corticosteroids. She had an episode of acute bacterial sinusitis 2 week ago and received the appropriate therapy. Pelvic examination shows an erythematous vulva and a thick, adherent, "cottage cheeselike" vaginal discharge. The rest of the physical examination is within normal limits. Microscopic examination of the vaginal discharge reveals budding cells. Which of the following is the most likely underlying cause of her current condition?
    • A. 

      Decreased thickness of the vaginal epithelium

    • B. 

      Decreased glycogen concentration in the vaginal epithelium

    • C. 

      Decreased number of Gram-positive bacteria in the vagina

    • D. 

      Increased alkaline secretions by the cervical mucosa

    • E. 

      Depressed T-lymphocyte response to mucosal stimuli

  • 18. 
    A 34-year-old woman comes to the physician complaining of fever, dysuria, and flank pain. Her temperature is 37.8 C (100 F), blood pressure is 122/78 mm Hg, and pulse is 84/min. Physical examination elicits suprapubic and costovertebral angle tenderness. Urine dipstick analysis reveals positive leukocyte esterase and nitrite. A subsequent urine culture grows colonies of motile Gram-negative rods demonstrating a green metallic sheen on eosin methylene blue (EMB} agar and hemolysis on blood agar. Which of the following is the most important bacterial factor responsible for this patient's condition?
    • A. 

      Capsule

    • B. 

      Heat-labile enterotoxin

    • C. 

      O antigen

    • D. 

      Fimbrial antigen

    • E. 

      Lipid A

  • 19. 
    A 23-year-old Caucasian female is brought to the ER with fever, vomiting, diarrhea and muscle pain. Her blood pressure is 90/50 mm Hg and pulse is 120/min. Physical examination reveals erythroderma, and pelvic exam reveals a tampon in the vagina. The activation of which of the following cells is primarily responsible for this patient's condition?
    • A. 

      Mast cells and eosinophils

    • B. 

      Basophils and macrophages

    • C. 

      Neutrophils and B lymphocytes

    • D. 

      Macrophages and T lymphocytes

    • E. 

      Platelets and mast cells

  • 20. 
    A 72-year-old man is brought to the emergency department from a skilled nursing facility because of altered mental status, skin flushing, and a high fever. His blood pressure is 60/20 mmHg, and heart rate is 11 O/min. If blood cultures are positive for E coli, which of the following is the most likely source of bacteremia in this patient?
    • A. 

      Small intestine

    • B. 

      Colon

    • C. 

      Urinary tract

    • D. 

      Biliary tree

    • E. 

      Lungs

    • F. 

      Oropharynx

    • G. 

      Skin

  • 21. 
    A 59-year-old female is brought to the ER with fever, skin flushing, and an altered level of consciousness. Her blood pressure is 50/20 mmHg, and her heart rate is 120/min. If blood cultures are positive for E coli, which of the following bacterial factors is most likely responsible for this patient's current condition?
    • A. 

      Capsule

    • B. 

      Heat-stable exotoxin

    • C. 

      O antigen

    • D. 

      Fimbrial antigen

    • E. 

      Lipid A

    • F. 

      Flagellar antigen

  • 22. 
    A 39 year-old paraplegic man with an indwelling bladder catheter presents to the emergency room complaining of twenty-four hours of rigors, nausea, and vomiting. His temperature is 38.9° C (102.0° F). Urinalysis shows 3+ leukocyte esterase and numerous white blood cells. Urine and blood cultures grow non-lactose fermenting gram-negative bacilli. Which of the following pathogens is the most likely culprit?
    • A. 

      Escherichia coli

    • B. 

      Pseudomonas aeruginosa

    • C. 

      Klebsiella pneumoniae

    • D. 

      Staphylococcus saprophyticus

    • E. 

      Enterococcus cloacae

    • F. 

      Ureaplasma urealyticum

  • 23. 
    Genital examination of a 31-year-old female reveals yellow discharge from the cervical os that demonstrates abundant neutrophils on light microscopy. The patient will most likely experience which of the following as a sequela of this disease?
    • A. 

      Endometrial hyperplasia

    • B. 

      Hydatidiform mole

    • C. 

      Ovarian cancer

    • D. 

      Polycystic ovary syndrome

    • E. 

      Infertility

  • 24. 
    A 24-year-old female presents to your office with burning urination, urgency and frequency. She is sexually active. Urine cultures show catalase-positive, gram-positive cocci. The organism responsible for this patient's symptoms is most likely to be:
    • A. 

      Coagulase positive

    • B. 

      Hemolytic

    • C. 

      Novobiocin resistant

    • D. 

      DNase positive

    • E. 

      Yellow pigment producer

  • 25. 
    Group A Streptococci demonstrate significant resistance to phagocytic killing when placed in fresh human blood. This resistance can be most effectively overcome by adding antibodies to which of the following?
    • A. 

      Hyaluronate

    • B. 

      Protein M

    • C. 

      Streptolysin O

    • D. 

      DNase

    • E. 

      Streptokinase

    • F. 

      Teichoic acid

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