USMLE Microbiology - Part 2

20 Questions | By Chachelly | Last updated: Mar 20, 2022 | Total Attempts: 390

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1.

A 4-year-old boy presents to the pediatric emergency department with the classic meningitis triad of fever, headache, and nuchal rigidity. A lumbar puncture is performed and analysis of the fluid shows an increase in polymorphonuclear cells, an increased protein level, and a decreased glucose level. Which of the following is the most common cause of meningitis in a child of this age with this clinical picture?
- A.
  
  Enteroviruses
- B.
  
  Haemophilus infl uenzae type B
- C.
  
  Herpes simplex virus
- D.
  
  Listeria species
- E.
  
  Streptococcus pneumoniae
2.

A 32-year-old man presents to his doctor with painful urination and a purulent urethral discharge. The image shows cells that have been cultured from this discharge. Which of the following is the treatment of choice for this infection?
- A.
  
  Azithromycin
- B.
  
  Ceftriaxone
- C.
  
  Fluconazole
- D.
  
  Penicillin
- E.
  
  Vancomycin
3.

A 43-year-old man presents with fl u-like symptoms, fevers, chills, and a productive cough. Physical examination is remarkable for pleuritic chest pain. On questioning, the patient says that he has just spent the last week on vacation in Central America. Cultures taken from the patient show a broad-based budding fungus. It is concluded that the man has systemic blastomycosis infection. Which of the following agents is the most appropriate treatment for this patient?
- A.
  
  Amphotericin B
- B.
  
  Fluconazole
- C.
  
  Itraconazole or potassium iodide
- D.
  
  Sodium stibogluconate only
- E.
  
  Topical miconazole or selenium sulfide
4.

73-year-old woman steps on a rusty nail while gardening in her back yard. A neighbor drives her to the emergency department, where her wound is cleaned and bandaged. A complete history and review of her medical chart indicates that her vaccinations are not up to date, and she requires one vaccination and a shot of the appropriate immunoglobulin as prophylaxis against infection. What is the mechanism of toxicity of the organism for which she was vaccinated?
- A.
  
  ADP-ribosylation of a G protein, increasing chloride secretion
- B.
  
  ADP-ribosylation of an elongation factor, causing disrupted protein synthesis
- C.
  
  Binding to the MHC II receptor and T-lymphocyte receptor, causing cytokine synthesis
- D.
  
  Blocking release of the inhibitory neurotransmitter glycine
- E.
  
  Blocking the release of acetylcholine
- F.
  
  Lysis of RBCs
- G.
  
  Stimulation of guanylate cyclase
5.

A 50-year-old man develops nonbloody watery diarrhea while working as an aid worker in a refugee camp in Bangladesh. He arrived in the area 2 days ago. A stool smear shows no WBCs. He subsequently develops dehydration and electrolyte abnormalities leading to cardiac and renal failure. Which of the following organisms is the most likely cause of this man’s enterocolitis?
- A.
  
  Clostridium diffi cile
- B.
  
  Giardia lamblia
- C.
  
  Helicobacter pylori
- D.
  
  Salmonella species
- E.
  
  Vibrio cholerae
6.

Twenty-four hours after placement of a catheter, a hospitalized patient develops a fever and chills. Within 1 hour her systolic blood pressure falls 30 points and she develops swelling in her extremities. Despite valiant efforts by the hospital staff, the patient dies. X-ray of the patient’s lungs taken only hours before she passed away shows pulmonary edema. Which of the following mediators of this patient’s disease process is most likely responsible for the pathology described?
- A.
  
  C3a
- B.
  
  C5a
- C.
  
  Hageman factor
- D.
  
  γ-Interferon
- E.
  
  Interleukin-1
- F.
  
  Nitric oxide
7.

A 31-year-old pregnant woman comes to the physician because of painful vesicular lesions that have recently appeared on her genitalia. A positive result on which of the following diagnostic tests would mean that her baby is at risk for congenital anomalies?
- A.
  
  Anti-hepatitis B surface antibody test
- B.
  
  Giemsa stain for cytoplasmic inclusions
- C.
  
  Monospot test
- D.
  
  Tzanck smear for multinucleated giant cells
- E.
  
  Weil-Felix test
8.

A 13-year-old girl who returned a few days ago from a school camping trip in North Carolina is home ill from school. She tells her parents that she has a headache and the chills. Over the next few days, she develops a rash that begins on her palms and soles, but spreads inward to her wrists and ankles and then to her trunk. Her worsening condition leads her parents to take her to the emergency department, where a blood test reveals antibodies that react with the Proteus antigen. This patient is most likely infected with which of the following?
- A.
  
  Borrelia burgdorferi
- B.
  
  Coxiella burnetti
- C.
  
  Coxsackievirus A
- D.
  
  Rickettsia rickettsii
- E.
  
  Rickettsia typhi
- F.
  
  Treponema pallidum
9.

A 53-year-old obese man with poorly controlled non-insulin-dependent diabetes mellitus presents with fever to 39.6° C (103.2° F), jaundice, hypotension, and acute onset of right upper quadrant pain. Right upper quadrant imaging shows multiple gallstones and cholecystitis. Urgent cholecystectomy is performed, and subsequent gall bladder fl uid and blood cultures grow aerobic, non-lactose-fermenting, oxidasepositive, gram-negative rods. Blood tests show: Hematocrit: 29% WBC count: 14,700/mm3 Platelet count: 76,000/mm3 D-dimer: 8500 ng/mL Fibrinogen levels: low Microscopic inspection of peripheral blood smear shows schistocytes and multiple helmet cells. Clinically, there is no evidence of active bleeding. What is the most appropriate treatment for this patient’s coagulopathy? International Normalized Ratio: 3.2
- A.
  
  Amoxicillin
- B.
  
  Aztreonam
- C.
  
  Fresh frozen plasma
- D.
  
  Vancomycin
- E.
  
  Vitamin K
10.

A 22-year-old woman presents to the physician with vaginal itching and burning. On examination, she has a foul-smelling greenish discharge. A swab sample is taken and a wet mount slide is prepared; results are shown in the image. Which of the following medications should be prescribed for this patient?
- A.
  
  Metronidazole
- B.
  
  Nifurtimox
- C.
  
  Quinine
- D.
  
  Sodium stibogluconate
- E.
  
  Sulfadiazine and pyrimethamine
11.

A 40-year-old man goes on a camping vacation with his family. One day after swimming in a freshwater lake near the camp site, he develops nausea and vomiting and starts to behave irrationally. His family takes him to the emergency department, where blood samples are taken and a spinal tap is performed. He is diagnosed with a rapidly progressing meningoencephalitis and dies shortly thereafter. Which of the following protozoa was most likely the cause of the man’s illness?
- A.
  
  Cryptosporidium species
- B.
  
  Entamoeba histolytica
- C.
  
  Leishmania donovani
- D.
  
  Naegleria fowleri
- E.
  
  Plasmodium falciparum
12.

A 54-year-old man presents to the clinic with scleral icterus, hepatosplenomegaly, ascites, and a history of episodes of jaundice over the past 3 years. He was involved in an auto accident when he was 21 years old, for which he required surgery and blood transfusions. Laboratory tests show: Aspartate aminotransferase: 734 U/L Alanine aminotransferase: 846 U/L Direct bilirubin: 0.1 mg/dL Indirect bilirubin: 7.6 mg/dL Assuming a viral etiology, which of the following is the most likely cause of this patient’s illness?
- A.
  
  Hepatitis A
- B.
  
  Hepatitis C
- C.
  
  Hepatitis D
- D.
  
  Hepatitis E
- E.
  
  Hepatitis G
13.

A 19-year-old college student presents to his family physician with a 1-week history of fever, headache, and painful exudative pharyngitis. Physical examination shows signifi cant lymphadenopathy of the cervical nodes and hepatosplenomegaly. Laboratory studies show a WBC count of 15,000/mm3 with 55% lymphocytes. A heterophile antibody test is positive. Which of the following is the most likely cause of this patient’s symptoms?
- A.
  
  Cytomegalovirus
- B.
  
  Epstein-Barr virus
- C.
  
  HIV infection
- D.
  
  Streptococcus pneumoniae
- E.
  
  Toxoplasma gondii
14.

A 36-year-old man comes to the physician complaining of an aching back, high fever, and vomiting of dark material. He is obviously ill and states that he has felt very poorly for approximately 1 week. Physical examination shows that the patient has a temperature of 39° C (102.2° F) and icteric sclera. The patient recently returned from a trip on safari in Africa. If a liver biopsy were done, it would show the following pathology. What are the names of the eosinophilic globules shown in this image?
- A.
  
  Councilman bodies
- B.
  
  Döhle bodies
- C.
  
  Negri bodies
- D.
  
  Pappenheimer bodies
- E.
  
  Weibel-Palade bodies
15.

A 56-year-old man presents to the emergency department with sharp retrosternal pain radiating to his back and arms. The patient is sitting up and leaning forward. He states that the pain is less severe in this position and worsens when he lies down and takes a deep breath. He also indicates that he recently recovered from a fever and a cold. On physical examination a scratchy, leathery sound is heard at the lower left sternal border. An ECG is done and confi rms the diagnosis. Which of the following microorganisms is the most likely cause of this condition?
- A.
  
  Coronavirus
- B.
  
  Coxsackievirus
- C.
  
  Cytomegalovirus
- D.
  
  Epstein-Barr virus
- E.
  
  Staphylococcus aureus
16.

A 28-year-old man comes to the physician because of worsening muscle weakness that began in his legs and feet 3 days ago, and has now spread to his arms and hands. Other than having a fl u-like illness 2 weeks ago, the patient has been in good health. Cerebrospinal fl uid analysis shows an increased protein concentration, a normal cell count, and a normal glucose level. An infection with which of the following organisms is the most likely cause of the nervous system syndrome described in this patient?
- A.
  
  Candida albicans
- B.
  
  Legionella pneumophila
- C.
  
  Mycoplasma pneumoniae
- D.
  
  Pseudomonas aeruginosa
- E.
  
  Streptococcus pneumoniae
17.

A 55-year-old man comes to his physician with a tender, swollen, and erythematous left knee. He has limited range of motion in his leg. On aspiration of the synovial fl uid from his knee, the fl uid is found to be yellow and cloudy and has 150,000 neutrophils/mm3. Gram stain of the aspirate shows gram-positive cocci in clusters. The organism most likely responsible for this patient’s symptoms has which of the following properties?
- A.
  
  Catalase-positive and coagulase-negative
- B.
  
  Catalase-positive and coagulase-positive
- C.
  
  Glycoprotein capsule
- D.
  
  α-Hemolysis
- E.
  
  Soluble in bile
18.

A family who recently emigrated from Romania brings their 7-year-old child to the pediatrician with complaints of conjunctivitis and periorbital swelling. The child has had coughing with a runny nose and high fever for 3 days. Small lesions with blue-white centers are seen in his oral cavity. Which of the following is the most likely cause of this child’s symptoms?
- A.
  
  Diphtheria
- B.
  
  Pertussis
- C.
  
  Roseola
- D.
  
  Rubella
- E.
  
  Rubeola
19.

A 34-year-old woman newly diagnosed with HIV infection is unable to access antiretroviral medications. She is aware that if untreated, her disease will progress and make her susceptible to different infections. She inquires about the natural course her disease may take and the different infections she might acquire. Which of the following conditions is most likely to manifest only when the T cell count drops below 50/mm3?
- A.
  
  Disseminated Mycobacterium aviumintracellulare
- B.
  
  Herpes simplex virus infection
- C.
  
  Herpes zoster infection
- D.
  
  Oral thrush
- E.
  
  Pneumonia due to Pneumocystis jiroveci
- F.
  
  Toxoplasmosis brain lesion
20.

An 8-year-old boy is brought to his pediatrician by his parents because of a fever and a sore throat. On examination, he has tonsillar exudates and swollen, tender anterior cervical nodes. His parents report no history of cough. Gram stain of the tonsillar exudate reveals gram-positive cocci. Which of the following describes the organism most likely causing this patient’s symptoms?
- A.
  
  Catalase-negative, α-hemolytic, optochinresistant
- B.
  
  Catalase-negative, α-hemolytic, optochinsensitive
- C.
  
  Catalase-negative, β-hemolytic, bacitracinresistant
- D.
  
  Catalase-negative, β-hemolytic, bacitracinsensitive
- E.
  
  Catalase-positive, coagulase-negative, novobiocin- resistant
- F.
  
  Catalase-positive, coagulase-negative, novobiocin- sensitive