Which organism is most likely to be isolated in cultures from the anterior nares of healthcare workers?

• A. Bacillus cereus
• B. Streptococcus pneumoniae
• C. Staphylococcus aureus
• D. Staphylococcus saprophyticus

Answer: (C)

The anterior nares are a primary reservoir for Staphylococcus aureus, including both methicillin-susceptible and methicillin-resistant strains. Healthcare workers commonly carry this organism asymptomatically, which makes it the most likely to be recovered from nasal swabs in a hospital setting. Carriage in the nose facilitates transmission to patients or surfaces and can contribute to nosocomial infections if not managed.

Staphylococcus aureus is a Gram-positive coccus that appears in clusters and is coagulase-positive, a trait that helps distinguish it from other Staphylococcus species. In contrast, Streptococcus pneumoniae mainly colonizes the nasopharynx, especially in children; Bacillus cereus is primarily an environmental organism found in soil and contaminated food; Staphylococcus saprophyticus is a common cause of urinary tract infections and is not typically part of nasal flora. Hence, Staphylococcus aureus is the organism most likely to be isolated from the anterior nares of healthcare workers.