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Free notes, MCQs, tables & flowcharts for USMLE Step 3 Microbiology
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 patient is hospitalized for pneumonia. Gram-positive cocci in clusters are seen on sputum gram stain. Which of the following clinical scenarios is most commonly associated with this form of pneumonia?
AElderly patient who has trouble swallowing and poor dentition
BAn alcoholic with evidence of empyema and "currant jelly sputum"
CAn otherwise healthy young adult with a week of mild fatigue, chills, and cough
DHospitalized adult with development of pneumonia symptoms 2 weeks following a viral illness
EHIV positive adult with a CD4 count less than 150 and an impaired diffusion capacity
A 69-year-old man is brought to the emergency department by his wife because of fever, cough, diarrhea, and confusion for 2 days. He recently returned from a cruise to the Caribbean. He has a history of chronic obstructive pulmonary disease. He has smoked one pack of cigarettes daily for 40 years. His temperature is 39.1°C (102.4°F), pulse is 83/min, and blood pressure is 111/65 mm Hg. He is confused and oriented only to person. Physical examination shows coarse crackles throughout both lung fields. His serum sodium concentration is 125 mEq/L. Culture of the most likely causal organism would require which of the following mediums?
ACharcoal yeast extract agar
BEosin-methylene blue agar
CMannitol salt agar
DChocolate agar
EEaton agar
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