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

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

Answer: (B)

Staphylococcus aureus is most likely found in cultures from the anterior nares because this site is a primary reservoir for nasal carriage of S. aureus in healthy individuals, including healthcare workers. Many people carry the bacterium asymptomatically in their nose, making it a common source of transmission to patients in hospital settings. This organism has specific properties that favor colonization of the nasal mucosa, such as adherence factors that help it attach to the lining of the nose and persist there over time.

The other organisms listed don’t typically inhabit the anterior nares as stable nasal flora. Bacillus cereus is an environmental bacterium more often associated with soil and food contamination. Streptococcus pneumoniae can colonize the nasopharynx, especially in children, but it is not a common stable anterior nares commensal in healthy adults. Staphylococcus saprophyticus is primarily associated with the genitourinary tract and urinary infections rather than nasal carriage.