USMLE Microbiology Prt 4

25 Questions | Total Attempts: 330

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USMLE Microbiology Prt 4

Questions and Answers
  • 1. 
    An Hispanic male is referred to the dermatology clinic of a major medical center. On physical examination, the man has several disfiguring lesions on his face and there is loss of cutaneous sensation to fine touch, pain, and temperature. An acid-fast organism is observed in scrapings from a skin lesion. Which of the following organisms is the most likely cause of this patient's disease?
    • A. 

      Bartonella henselae

    • B. 

      Listeria monocytogenes

    • C. 

      Mycobacterium avium-intracellulare

    • D. 

      Mycobacterium leprae

    • E. 

      Nocardia asteroides

  • 2. 
    A patient develops fever, shortness of breath, and appears to be quite ill. X-ray demonstrates bilateral interstitial lung infiltrates. Bronchial washings demonstrate small "hat-shape" organisms visible on silver stain within alveoli. Which predisposing condition is most likely to be present in this patient?
    • A. 

      AIDS

    • B. 

      Congestive heart failure

    • C. 

      Pulmonary embolus

    • D. 

      Rheumatoid arthritis

    • E. 

      Systemic lupus erythematosus

  • 3. 
    A 23-year-old man develops explosive watery diarrhea with blood, fecal leukocytes, and mucus approximately 3 days after eating chicken that was improperly cooked. Comma-shaped organisms were found in the fecal smear along with red blood cells and leukocytes. Which of the following pathogens is the most likely cause of these symptoms?
    • A. 

      Campylobacter jejuni

    • B. 

      Enterotoxigenic E. coli

    • C. 

      Shigella sonnei

    • D. 

      Staphylococcus aureus

    • E. 

      Vibrio cholera

  • 4. 
    A 37-year-old, intravenous drug-abusing male presents with fever and chills. Blood cultures are positive for Staphylococcus aureus. He develops central nervous system symptoms, and a cerebral abscess is suspected. Which part of the brain is most often affected by septic emboli in patients with infective endocarditis?
    • A. 

      Brainstem

    • B. 

      Cerebellum

    • C. 

      Frontal lobe

    • D. 

      Occipital lobe

    • E. 

      Parietal lobe

  • 5. 
    A 33-year-old male with AIDS and a history of shingles develops a severe, multifocal encephalitis. Therapy is instituted with acyclovir, but the man dies on the fourth day of his hospital admission. Which of the following viruses is the most likely cause of his encephalitis?
    • A. 

      Cytomegalovirus

    • B. 

      Herpes simplex type I

    • C. 

      Herpes simplex type II

    • D. 

      Herpes zoster-varicella

    • E. 

      Measles virus

  • 6. 
    A 35-year-old male undergoes an appendectomy. Several days later, an abscess has formed at the surgical site. It does not improve with administration of a cephalosporin, but does respond to nafcillin. The infecting organism most likely produced an enzyme that would hydrolyze which bond in the above molecule?
    • A. 

      A

    • B. 

      B

    • C. 

      C

    • D. 

      D

  • 7. 
    A 10-year-old boy is attending summer camp in Texas. After 2 weeks of camp, he complains of a sore throat, headache, cough, and malaise. On physical examination, he also has a low-grade fever and keratoconjunctivitis. Within hours, several other campers and counselors visit the infirmary with similar symptoms. All of the patients had been swimming in the camp swimming pool. Eventually, more than 50% of the camp complain of symptoms similar to the initial case that last 5 to 7 days. Which of the following is the most likely causative organism?
    • A. 

      Adenovirus

    • B. 

      Chlamydia

    • C. 

      Gram-negative diplococcus

    • D. 

      Gram-positive enterococcus

    • E. 

      Herpesvirus

  • 8. 
    A 35-year-old sexually active male presents to his internist with a painless penile vesicle. Physical exam reveals inguinal lymphadenopathy. The infecting organism is definitively diagnosed and is known to exist in distinct extracellular and intracellular forms. Which of the following is the most likely pathogen?
    • A. 

      Calymmatobacterium granulomatis

    • B. 

      Chlamydia trachomatis

    • C. 

      Haemophilus ducreyi

    • D. 

      Neisseria gonorrhoeae

    • E. 

      Treponema pallidum

  • 9. 
    A 45-year-old white male with a history of alcohol abuse and periodontal disease is brought to the emergency room for a spiking fever and chills. Physical examination is significant for signs of lung consolidation. A chest x-ray shows a cavity in the right lower lobe that has an air/fluid level. A transtracheal aspiration is performed and the specimen is submitted to the laboratory for routine cultures and Gram's stain. Based upon the clinical presentation, which of the following would be the most likely finding?
    • A. 

      Anaerobic bacteria

    • B. 

      Aspergillus fumigatus

    • C. 

      Entamoeba histolytica

    • D. 

      Staphylococcus aureus

    • E. 

      Streptococcus pyogenes

  • 10. 
    A traveler in Bogota, Colombia drinks a glass of fruit juice with ice cubes made from tap water. E. coli contaminating the water supply grow in the traveler's intestine and synthesize a protein that causes his intestinal epithelium to overproduce cyclic AMP, resulting in a watery diarrhea. This syndrome is typical of which of the pathogenic strains of E. coli?
    • A. 

      Enteroaggregative

    • B. 

      Enterohemorrhagic

    • C. 

      Enteroinvasive

    • D. 

      Enteropathogenic

    • E. 

      Enterotoxigenic

  • 11. 
    Zygomycosis, a destructive fungal infection of the sinuses, is likely to reach the brain by which of the following routes?
    • A. 

      Cavernous sinus

    • B. 

      External carotid artery

    • C. 

      Internal carotid artery

    • D. 

      Superior sagittal sinus

    • E. 

      Superior vena cava

  • 12. 
    A farmer's wife develops abdominal pain and diarrhea, followed several days later by fever, periorbital edema, eosinophilia, and myalgia. She does not remember eating anything unusual recently, but notes that she does make her own pork sausage. Which of the following techniques would be most helpful for the diagnosis of this patient?
    • A. 

      Gastric biopsy

    • B. 

      Muscle biopsy

    • C. 

      Scotch tape test

    • D. 

      Stool for ova

    • E. 

      Stool for protozoal parasites

  • 13. 
    A 70-year-old man with a history of prostate cancer presents with a chief complaint of pain on the right side of his chest for the past several days. He has been receiving external beam radiation to spinal metastases of his prostate cancer for the past several weeks. On examination, there is marked tenderness along the right side of the chest wall in a 4-6 cm stripe from the midline to the flank. Multiple small vesicular lesions are visible in this area on an erythematous base. Some of the lesions are fluid-filled, and some are crusted. How do members of the virus family responsible for his condition produce messenger RNA?
    • A. 

      By direct translation from the genome

    • B. 

      By producing a double-stranded DNA intermediate

    • C. 

      By producing a negative sense intermediate

    • D. 

      By producing a positive sense intermediate

    • E. 

      By transcribing the genomic DNA

    • F. 

      By transcription from proviral DNA

    • G. 

      The genomic RNA is used directly on the ribosome

  • 14. 
    A 66-year-old man with urinary retention secondary to prostatic hyperplasia develops a spiking fever and tachypnea. Physical exam reveals intercostal muscle retractions and bilateral inspiratory crackles. A chest x-ray exhibits bilateral interstitial and alveolar infiltrates. Arterial blood gases demonstrate severe hypoxemia. Blood cultures would most likely reveal
    • A. 

      Gram-negative diplococci

    • B. 

      Gram-negative rods

    • C. 

      Gram-positive cocci

    • D. 

      Gram-positive diplococci

    • E. 

      Gram-positive rods

  • 15. 
    A sexually active 25-year-old man develops epididymitis and orchitis. Needle biopsy demonstrates a prominent leukocytic infiltrate with numerous neutrophils. Which of the following organisms is the most likely cause of this man's infection?
    • A. 

      Escherichia coli

    • B. 

      Mycobacterium tuberculosis

    • C. 

      Neisseria gonorrhoeae

    • D. 

      Pseudomonas sp.

    • E. 

      Treponema pallidum

  • 16. 
    Which of the following organisms is the most common cause of community-acquired pneumonia?
    • A. 

      Chlamydia pneumoniae

    • B. 

      Haemophilus influenzae

    • C. 

      Mycoplasma pneumoniae

    • D. 

      Staphylococcus aureus

    • E. 

      Streptococcus pneumoniae

  • 17. 
    A patient with a history of chronic diarrhea and bloody stools presents to the emergency department with right upper quadrant pain and fever. Physical examination demonstrates a large, tender liver. Which of the following would be most likely to have caused the patient's problems?
    • A. 

      Cryptosporidium parvum

    • B. 

      Entamoeba histolytica

    • C. 

      Giardia lamblia

    • D. 

      Isospora belli

    • E. 

      Trichomonas vaginalis

  • 18. 
    A neonate is born in very poor condition, with a severe, generalized encephalitis. Which of the following viruses is the most likely pathogen in this setting?
    • A. 

      Eastern equine encephalitis virus

    • B. 

      Herpes simplex type II

    • C. 

      Herpes zoster-varicella virus

    • D. 

      Poliomyelitis virus

    • E. 

      St. Louis encephalitis virus

  • 19. 
    A 15-year-old high school student and several of her friends ate lunch at a local Chinese restaurant. They all were served the daily luncheon special, which consisted of sweet and sour pork with vegetables and fried rice. All of the girls developed nausea, vomiting, abdominal pain, and diarrhea within 6 hours of eating lunch. Which of the following is the most likely cause of these symptoms?
    • A. 

      Bacillus cereus

    • B. 

      Clostridium botulinum

    • C. 

      Clostridium perfringens

    • D. 

      EHEC (Enterohemorrhagic E. coli)

    • E. 

      Staphylococcus aureus

    • F. 

      Vibrio cholerae

  • 20. 
    A 29-year-old news correspondent returns from covering an earthquake and its aftermath in a third world country. The man feels tired and has sore muscles, so he consults a physician, who examines him, but decides not to admit him to the hospital. The man subsequently develops a disabling illness complicated by severe anemia, pulmonary edema, renal failure, and shock. Which of the following organisms is the most likely pathogen?
    • A. 

      Babesia microti

    • B. 

      Plasmodium falciparum

    • C. 

      Plasmodium malariae

    • D. 

      Plasmodium ovale

    • E. 

      Plasmodium vivax

  • 21. 
    A 9-month-old infant is brought to the Health Department to receive the second dose of OPV (oral polio vaccine) 2 weeks after the first vaccination. The child has mild diarrhea, so the decision is made to defer further immunizations. Bacteriologic examination of a stool culture is unremarkable; however, a small, single-stranded, positive RNA virus is isolated from the specimen. This same agent was isolated from sewage effluent the preceding week. The viral isolate was not inactivated by ether. Which of the following viruses was most likely isolated?
    • A. 

      Adenovirus

    • B. 

      Hepatitis C

    • C. 

      Parvovirus B19

    • D. 

      Poliovirus

    • E. 

      Rotavirus

  • 22. 
    A 24-year-old male Asian immigrant presents with an ulcerative genital lesion. The lesion first appeared 1 month ago as a papule with an erythematous base, which eventually became ulcerated and painful. On physical examination, the man is afebrile. A tender ulcerative lesion is present on his prepuce, and inguinal adenopathy is evident. Which of the following would be the most likely microscopic finding in a scraping from the rash?
    • A. 

      Epithelial cells with intranuclear inclusion bodies

    • B. 

      Iodine-staining intracellular inclusion bodies

    • C. 

      Koilocytotic squamous epithelial cells

    • D. 

      Neutrophils containing gram-negative diplococci

    • E. 

      Pleomorphic gram-negative rods in a "school of fish" pattern

    • F. 

      Spirochetes visible by darkfield microscopy

  • 23. 
    A burn patient at the university hospital has been progressively deteriorating. He was catheterized for several days and developed a severe pneumonia, for which he was intubated and is now ventilator-dependent. A gram-negative, non-fermenting rod is isolated from his sputum. It produces a blue-green pigment on growth media and has a grape-like fruity odor. The organism most likely isolated is
    • A. 

      Escherichia coli

    • B. 

      Klebsiella pneumoniae

    • C. 

      Legionella pneumophila

    • D. 

      Pseudomonas aeruginosa

    • E. 

      Serratia marcescens

  • 24. 
    A 57-year-old fisherman with a history of alcoholism is hospitalized in Gulfport, Mississippi with a 1-day history of severe, watery diarrhea after eating several raw oysters. He is badly dehydrated on admission, and within 12 hours, he becomes severely hypotensive and dies. Which of the following pathogens is the most likely cause of this man's death?
    • A. 

      Citrobacter diversus

    • B. 

      Enterotoxigenic E. coli

    • C. 

      Providencia stuartii

    • D. 

      Vibrio cholerae

    • E. 

      Vibrio vulnificus

  • 25. 
    A 38-year-old AIDS patient presents to his physician's office in Kansas City, Missouri, complaining of fever for the past week and an increasing headache. He also states that sunlight hurts his eyes and that he has been feeling nauseated and weak. His past medical history is significant for Pneumocystis pneumonia and a total CD4 count of 89. Current medications are trimethoprim/sulfa and indinavir. Cerebrospinal fluid (CSF) reveals 4 WBC, and budding encapsulated yeast forms grow on Sabouraud's agar. Which of the following is an accurate description of the morphology of the infectious form of the organism responsible for the man's illness?
    • A. 

      Broad-based, budding yeasts

    • B. 

      Budding yeasts in a "pilot's wheel" arrangement

    • C. 

      Cylindrical arthroconidia

    • D. 

      Encapsulated budding yeasts

    • E. 

      Filamentous molds

    • F. 

      Septate hyphae with microconidia and macroconidia

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