Prevalence of Staphylococcus aureus and lack of its lytic bacteriophages in the anterior nares of patients and healthcare workers at a rural clinic.

BACKGROUND: Nearly 30% of people in the United States are colonized with Staphylococcus aureus and 1% to 2% with methicillin-resistant Staphylococcus aureus (MRSA) in the anterior nares. However, it is not known if lytic bacteriophages against S. aureus are present in the anterior nares, and if they are, what the prevalence rate is, or if they interfere with S. aureus colonization. The aim of this study was to determine the prevalence of nasal carriage of S. aureus and MRSA and to screen for S. aureus lytic bacteriophages in healthcare environment workers and ambulatory patients.
METHODS: We enrolled 202 individuals into this study. The anterior nares were swabbed to isolate S. aureus, MRSA, and any lytic S. aureus bacteriophages that may be present. Putative S. aureus colonies on blood agar plates were identified using gram stain, catalase and coagulase tests, and confirmed by S. aureus-specific PCR. Presence of staphylococcal lytic bacteriophages were screened by a plaque assay technique using a methicillin-sensitive reference S. aureus strain ATCC 29213.
RESULTS: Of the 49 (24%) individuals who screened positive for S. aureus, two (1%) were positive for MRSA. None of the samples were positive for lytic bacteriophages against S. aureus. Subgroup analysis found no significant difference in the prevalence of S. aureus in the house staff compared to other healthcare environment workers or ambulatory patients of the clinic. Similarly, no significant difference in colonization was noted across the population with respect to age, sex, body mass index, or presence of diabetes mellitus.
CONCLUSION: The prevalence of nasal carriage of S. aureus and MRSA in the studied population was 24% and 1%, respectively, similar to the rate of prevalence in the United States. The study also showed that the anterior nares do not seem to harbor lytic bacteriophages against S. aureus.