Bacteriology USMLE Step 1 Practice Question
A 43-year-old man with a 20-year history of alcohol use disorder presents to the hospital with acute pancreatitis complicated by sepsis. On hospital day 3, he develops a high fever (39.5°C), productive cough with purulent sputum, and worsening hypoxia requiring supplemental oxygen. Sputum culture is obtained. Gram staining of the sputum reveals gram-positive cocci in clusters. Culture on blood agar grows golden-yellow colonies within 24 hours. The isolate is catalase-positive, coagulase-positive, and ferments mannitol. Which of the following characteristics of this organism's cell wall composition best explains its gram-positive staining pattern?
Answer choices
- AHigh concentration of peptidoglycan in a thick, multilayered cell wallCorrect answer
- BPresence of lipopolysaccharide in the outer membrane
- CHigh content of mycolic acids with branched hydrocarbon chains
- DExtensive lipoteichoic acid anchoring to the peptidoglycan layer
- EPresence of porins that facilitate crystal violet uptake
- FLow permeability of the cell wall to lipophilic dyes
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