An active intravenous drug abuser presents to the emergency depament with fever of 5 days duration, a cough which is occasionally productive of blood, and pleuritic chest pain. Petechiae are present in his mouth and conjunctiva, and small linear hemorrhages are visible under his fingernails. Which of the following test results would MOST likely confirm the identity of the causative agent?
Correct Answer: Blood culture of a coagulase-positive, catalase positive, gram-positive coccus
Description: The patient is exhibiting the classic signs of acute bacterial endocarditis. In intravenous drug abusers, Staphylococcus aureus is the most common causative agent, because it is the most common normal flora organism on the skin of these patients, and is the classic description of this species. Catalase positivity distinguishes the genus Staphylococcus from Streptococcus, and Staphylococcus aureus is the only coagulase positive member of its genus. Antibodies to p24 capsid antigen would be likely in an HIV-positive drug abuser, rather than a patient with endocarditis. Trichinella spiralis can cause splinter hemorrhages during the larval migration period, but would not be the most likely agent given the other symptoms. Staphylococcus epidermidis is a catalase-positive, novobiocin-sensitive, gram-positive coccus. It is sometimes implicated in subacute bacterial endocarditis, but is less common as a causative agent in drug abusers than in normal individuals.
Category:
Microbiology
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