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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 62-year-old woman presents to the emergency department for evaluation of a spreading skin infection that began from an ulcer on her foot. The patient has type 2 diabetes mellitus that is poorly controlled. On examination, there is redness and erythema to the lower limb with skin breakdown along an extensive portion of the leg. The patient’s tissues separate readily from the fascial plane, prompting a diagnosis of necrotizing fasciitis. What is the exotoxin most likely associated with this patient’s presentation?
AStreptococcal pyogenic exotoxin A
BTSST-1
CDiphtheria toxin
DExfoliative toxin
EStreptococcal pyogenic exotoxin B
A 65-year-old man presents with low-grade fever and malaise for the last 4 months. He also says he has lost 9 kg (20 lb) during this period and suffers from extreme fatigue. Past medical history is significant for a mitral valve replacement 5 years ago. His temperature is 38.1°C (100.6°F), respirations are 22/min, pulse is 102/min, and blood pressure is 138/78 mm Hg. On physical examination, there is a new onset 2/6 holosystolic murmur loudest in the apical area of the precordium. Which of the following organisms is the most likely cause of this patient’s condition?
AEnterococcus
BCandida albicans
CCoagulase-negative Staphylococcus spp.
DEscherichia coli
EPseudomonas aeruginosa
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