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Free notes, MCQs, tables & flowcharts for USMLE Step 3 Microbiology
A 50-year-old male presents to the emergency room complaining of fever, shortness of breath, and diarrhea. He returned from a spa in the Rocky Mountains five days prior. He reports that over the past two days, he developed a fever, cough, dyspnea, and multiple watery stools. His past medical history is notable for major depressive disorder and peptic ulcer disease. He takes omeprazole and paroxetine. He does not smoke and drinks alcohol on social occasions. His temperature is 102.8°F (39.3°C), blood pressure is 120/70 mmHg, pulse is 65/min, and respirations are 20/min. Physical examination reveals dry mucus membranes, delayed capillary refill, and rales at the bilateral lung bases. A basic metabolic panel is shown below: Serum: Na+: 126 mEq/L Cl-: 100 mEq/L K+: 4.1 mEq/L HCO3-: 23 mEq/L Ca2+: 10.1 mg/dL Mg2+: 2.0 mEq/L Urea nitrogen: 14 mg/dL Glucose: 90 mg/dL Creatinine: 1.1 mg/dL Which of the following is the most appropriate growth medium to culture the pathogen responsible for this patient’s condition?
AEaton’s agar
BBordet-Gengou agar
CThayer-Martin agar
DCharcoal yeast agar with iron and cysteine
ESorbitol-MacConkey agar
A 60-year-old man presents with fever and cough productive of rust-colored sputum and is diagnosed with community acquired pneumonia. The causative organism is isolated, and a Gram stain is shown in Figure 1. Which of the following most correctly describes additional features of the most likely causative organism?
ACatalase negative, alpha hemolytic, optochin sensitive
BCatalase positive, alpha hemolytic, optochin sensitive
CCatalase negative, alpha hemolytic, optochin resistant
DCatalase positive, beta hemolytic, optochin sensitive
ECatalase negative, beta hemolytic, optochin sensitive
A 24-year-old woman presents to the ED with symptoms of pelvic inflammatory disease despite being previously treated with azithromycin for chlamydial infection. Based on your clinical understanding about the epidemiology of PID, you decide to obtain a gram stain which shows a gram-negative diplococci. What is the next step in order to confirm the identity of the organism described?
APerform an RT-PCR
BCulture in TCBS agar
CCulture in Thayer-Martin media
DObtain an acid fast stain
ECulture in Bordet-Gengou agar
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