USMLE Microbiology Prt 8

25 Questions | Total Attempts: 221

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USMLE Quizzes & Trivia

Questions and Answers
  • 1. 
    A 33-year-old man in Arkansas presents to the local clinic with fever, chills, headache, and generalized myalgias and arthralgias. On physical examination, an ulcer with a black base is apparent on his right hand, and epitrochlear lymphadenopathy is noted. A careful history reveals that the man is a hunter and trapper, recently trapping and skinning rabbits. Which of the following organisms is the most likely cause of this man's illness?
    • A. 

      Borrelia

    • B. 

      Brucella

    • C. 

      Francisella

    • D. 

      Leptospira

    • E. 

      Listeria

  • 2. 
    A 28-year-old HIV-positive male complains of pain on swallowing. Physical examination is remarkable for white plaque-like material on his tongue and buccal mucosa, which is scraped and sent to the laboratory. Based on these findings, and on the laboratory results, the man is diagnosed with acquired immunodeficiency syndrome (AIDS). With which of the following agents is the man most likely infected?
    • A. 

      Candida albicans

    • B. 

      Cytomegalovirus

    • C. 

      Herpes simplex I

    • D. 

      Human herpesvirus 8

    • E. 

      Human papilloma virus

  • 3. 
    A 26-year-old obstetric patient becomes acutely ill during her first trimester with infectious mononucleosis-like symptoms, but her heterophil antibody test was negative. A careful history reveals that the family has two cats in the house. The appropriate laboratory tests indicate the expectant mother is infected with Toxoplasma gondii. Months later, the woman delivers a full term baby with no obvious signs of infection with the protozoan parasite. The best test to diagnose acute infection in the neonate would be a parasite-specific ELISA for which isotype of immunoglobulin?
    • A. 

      IgA

    • B. 

      IgE

    • C. 

      IgG 1

    • D. 

      IgG 4

    • E. 

      IgM

  • 4. 
    Which of the following organisms is a natural transformer?
    • A. 

      Escherichia coli

    • B. 

      Neisseria gonorrhoeae

    • C. 

      Plasmodium vivax

    • D. 

      Pseudomonas aeruginosa

    • E. 

      Staphylococcus aureus

  • 5. 
    Which of the following structures is found only in Gram-negative microorganisms?
    • A. 

      Cell envelope

    • B. 

      Exotoxin

    • C. 

      Peptidoglycan

    • D. 

      Periplasmic space

    • E. 

      Teichoic acids

  • 6. 
    A 23-year-old, ill-appearing woman comes to the emergency room with a fever. She notes the recent development of nausea, diarrhea, and a rash. Her last menstrual period began 3 days ago. Physical examination is remarkable for blood pressure of 90/45 mm Hg and heart rate of 120 beats per minute. A diffuse erythematous rash with areas of desquamation over the hands and feet is noted. Infection with which of the following agents is the most likely cause of these signs and symptoms?
    • A. 

      Clostridium perfringens

    • B. 

      HIV-1

    • C. 

      Shigella dysenteriae

    • D. 

      Staphylococcus aureus

    • E. 

      Staphylococcus epidermidis

  • 7. 
    A pregnant southeast Asian immigrant presents for prenatal care. Her past medical history is significant for a severe illness 3 years ago characterized by fatigue, nausea, anorexia, vomiting, jaundice, joint pains, and generalized skin lesions that slowly disappeared. She has felt well recently. Which of the following laboratory tests should be ordered to investigate the patient's past illness?
    • A. 

      Hepatitis B surface antigen (HBsAg)

    • B. 

      IgG cytomegalovirus (CMV) antibody levels

    • C. 

      IgM antibody to HBsAg

    • D. 

      IgM antibody to hepatitis B core antigen

    • E. 

      Quantitation of hepatitis A virus (HAV) IgM antibody

  • 8. 
    The rationale for giving prophylactic antibiotics at the beginning of a surgical procedure can be thought of as an attempt to prevent the bacteria from entering which of the following growth phases?
    • A. 

      Death phase

    • B. 

      Lag phase

    • C. 

      Log phase

    • D. 

      Phase of decline

    • E. 

      Stationary phase

  • 9. 
    A 10-year-old girl presents with sore throat and fever. She denies any cough or rhinorrhea. A throat culture grows bacitracin-sensitive bacterial colonies. The infecting organism would be protected from the lytic action of detergents by its...
    • A. 

      Keratin-like proteins in the spore coat

    • B. 

      Lipopolysaccharide in the outer membrane

    • C. 

      Peptidoglycan layer

    • D. 

      Periplasmic space

    • E. 

      Ca2+ chelators

  • 10. 
    An antibiotic, such as penicillin, which modifies cell wall synthesis, tends to be most effective during which phase of bacterial growth in a closed system?
    • A. 

      Lag phase

    • B. 

      Log phase

    • C. 

      Phase of decline

    • D. 

      Stationary phase

  • 11. 
    A 14-year-old patient is brought in by his parents because of a sore throat. On physical examination, he is febrile, and has pharyngeal erythema with a tonsillar abscess. A throat culture on sheep blood agar yields colonies of gram-positive cocci that are surrounded by a zone of complete hemolysis. The organism was also plated on mannitol salt agar; it grew well and caused the medium to turn yellow. Which of the following microorganisms is the most likely cause of the patient's illness?
    • A. 

      Corynebacterium diphtheriae

    • B. 

      Haemophilus influenzae

    • C. 

      Staphylococcus aureus

    • D. 

      Streptococcus salivarius

    • E. 

      Streptococcus pyogenes

  • 12. 
    A 14-year-old boy is brought to the emergency department by his parents because of high fever, headache, and stiff neck for the past 36 hours. He has become confused over the course of the morning. He uses no medications, has no allergies, and is not sexually active. On examination, he has a temperature of 38 C, moderate nuchal rigidity, and marked photophobia. Lumbar puncture is performed, and the cerebrospinal fluid shows: WBC 3500 with 95% PMNs, elevated protein, decreased glucose, and gram-positive cocci in pairs and short chains. By which of the following mechanisms does this organism mediate its attachment to the respiratory mucosa?
    • A. 

      Production of a C carbohydrate

    • B. 

      Production of a hemolytic exotoxin

    • C. 

      Production of a hyaluronic acid capsule

    • D. 

      Production of an IgA protease

    • E. 

      Production of an M protein

  • 13. 
    In a closed system, spores are formed during which of the following phases of bacterial growth?
    • A. 

      Decline phase

    • B. 

      Exponential phase

    • C. 

      Lag phase

    • D. 

      Log phase

    • E. 

      Stationary phase

  • 14. 
    A 33-year-old HIV-positive male complains of headache and blurred vision. Physical exam reveals papilledema and ataxia. Head CT is normal but CSF obtained by lumbar puncture reveals encapsulated organisms observable with India ink. What is the treatment of choice for this infection?
    • A. 

      Amphotericin B

    • B. 

      Isoniazid

    • C. 

      Ketoconazole

    • D. 

      Metronidazole

    • E. 

      Nystatin

  • 15. 
    A 37-year-old man is admitted to the hospital with shortness of breath, cyanosis, and fever. Chest x-ray films reveal consolidation of the right lower lobe with relative sparing of the remaining lobes. A clinical diagnosis of lobar pneumonia is made and supported by the results of sputum cultures. Which of the following is the genus of the bacterium most likely to be isolated from this patient's sputum?
    • A. 

      Haemophilus

    • B. 

      Klebsiella

    • C. 

      Streptococcus, alpha-hemolytic

    • D. 

      Streptococcus, beta-hemolytic

    • E. 

      Streptococcus, gamma-hemolytic

  • 16. 
    A 67-year-old man with moderate renal dysfunction presents with influenza-like symptoms. The patient also has a red macular rash that first appeared on the ankles, then spread centrally. He reports nausea, vomiting, and profound restlessness. He states that he was recently hiking with some friends in the mountains, about a week ago. Rickettsia rickettsiae is demonstrated by immunohistochemistry on skin biopsy. Which of the following agents would be most appropriate to treat this patient's infection?
    • A. 

      Demeclocycline

    • B. 

      Doxycycline

    • C. 

      Methacycline

    • D. 

      Oxytetracycline

    • E. 

      Tetracycline

  • 17. 
    A 33-year-old HIV-positive male complains of headache and blurred vision. Physical exam reveals papilledema and ataxia. Head CT is normal but CSF obtained by lumbar puncture reveals encapsulated organisms observable with India ink. Which of the following is true concerning this organism?
    • A. 

      It can also be identified with methenamine silver stain

    • B. 

      It consists of branching septate hyphae

    • C. 

      It exists as a mycelial form at room temperature and as yeast at 37° C

    • D. 

      It is an encapsulated nondimorphic yeast found worldwide

    • E. 

      It is a nonencapsulated dimorphic yeast that reproduces by budding

  • 18. 
    A 5-year-old child who has not had routine pediatric care develops a febrile disease with cough and a blotchy rash, and is brought to the emergency room. On physical examination, there is cervical and axillary lymphadenopathy. Also noted is an erythematous, maculopapular rash behind the ears and along the hairline, involving the neck and, to a lesser extent, the trunk. Examination of this patient's oropharynx would likely reveal which of the following lesions?
    • A. 

      Adherent thin, whitish patch on gingiva

    • B. 

      Cold sores on the lips

    • C. 

      Curdy white material overlying an erythematous base on the oral mucosa

    • D. 

      Large shallow ulcers on the oral mucosa

    • E. 

      Multiple small white spots on the buccal mucosa

  • 19. 
    Which of the following is associated with Babesiosis rather than with Ehrlichiosis or Lyme disease?
    • A. 

      A characteristic rash

    • B. 

      Arthritis of the knee

    • C. 

      Hemolytic anemia

    • D. 

      Macrophages containing intracellular organisms

    • E. 

      Transmission by ixodid ticks

  • 20. 
    A United Nations representative from a poor African country has an influenza-like illness that resolves in a few days. Less than a week later, however, he develops muscle pain, spasms, and sensory disturbances. Two days after this, flaccid paralysis occurs. Which of the following is most likely to be immediately life-threatening in this patient?
    • A. 

      Acute renal failure

    • B. 

      Bowel paralysis

    • C. 

      Fulminant liver failure

    • D. 

      Gastrointestinal bleeding

    • E. 

      Respiratory paralysis

  • 21. 
    Evaluation of an adult third world immigrant to this country demonstrates chronic headaches accompanied by chronic mild nuchal rigidity. Cerebrospinal fluid sampling demonstrates a chronic inflammatory infiltrate with lymphocytes, plasma cells, macrophages, and fibroblasts. Which of the following is the most likely etiologic agent?
    • A. 

      Herpes virus

    • B. 

      Mumps virus

    • C. 

      Mycobacterium tuberculosis

    • D. 

      Neisseria menigitidis

    • E. 

      Streptococcus pneumoniae

  • 22. 
    A 14-year-old girl with cystic fibrosis is admitted to the hospital with fever and shortness of breath, and is diagnosed with pneumonia. During a respiratory therapy session, she coughs up mucus that is distinctly greenish in color. Which of the following organisms should be suspected?
    • A. 

      Klebsiella pneumoniae

    • B. 

      Mycoplasma pneumoniae

    • C. 

      Pneumocystic carinii

    • D. 

      Pseudomonas aeruginosa

    • E. 

      Streptococcus pneumoniae

  • 23. 
    A truck driver was involved in a serious accident and received second- and third-degree burns over his body. He was placed in the burn unit and, on his twelfth day of his admission, developed a wound infection with a bluish-green exudate. Treatment with chloramphenicol and tetracycline was unsuccessful. A gram-negative, motile organism was isolated that was oxidase-positive, did not ferment lactose, sucrose, or glucose, but grew on MacConkey's agar and produced a fruity aroma on that medium. Which of the following organisms was most likely isolated?
    • A. 

      Candida albicans

    • B. 

      Clostridium perfringens

    • C. 

      Escherichia coli

    • D. 

      Klebsiella pneumoniae

    • E. 

      Proteus mirabilis

    • F. 

      Proteus vulgaris

    • G. 

      Pseudomonas aeruginosa

    • H. 

      Serratia marcescens

  • 24. 
    A 3-month-old infant presents with a 3-day history of fever, cough, and poor feeding. On examination, the baby appears ill and has a temperature of 102 F and a respiratory rate of 32. A chest x-ray film shows bilateral patchy infiltrates in the lungs. Which of the following is the most likely etiologic agent?
    • A. 

      Coronavirus

    • B. 

      Influenza type A

    • C. 

      Parainfluenza type 1

    • D. 

      Respiratory syncytial virus

    • E. 

      Rhinovirus

  • 25. 
    A 3-year-old girl with a history of hydrocephalus is brought to the neurologist by her parents with a severe headache and fever. The girl underwent a revision of a ventricular-peritoneal shunt 1 month ago, and the neurologist suspects that an infection has occurred. Which of the following organisms would most likely be isolated from the shunt tubing?
    • A. 

      Bacteroides fragilis

    • B. 

      Corynebacterium diphtheriae

    • C. 

      Escherichia coli

    • D. 

      Staphylococcus epidermidis

    • E. 

      Streptococcus pneumoniae

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