Nasal colonization with methicillin resistant Staphylococcus aureus (MRSA) is a potent risk factor for infection. It is not known why some people are persistently colonized, while other, similarly exposed, individuals are intermittently colonized or remain non-colonized. We hypothesized that the nasal microbiome may be protective against MRSA colonization for some individuals.
26 persistently MRSA-colonized subjects and 26 non-colonized controls matched for age, gender, race, long term care, diabetes, HIV infection, renal failure, nasal glucocorticoid use, and antibacterial therapy were identified by an active screening program. The nasal microbiota were analyzed with PCR amplification and sequencing of the 16S rRNA gene. Comparison of all variables across the groups was performed using stratified logistic regression to account for the 1 to 1 matching. Canonical discriminant analysis was performed to assess differences in bacterial community across the two groups. Competing organisms were co-cultured with MRSA in vitro.
There was a negative association between MRSA colonization and colonization with Streptococcus spp. At the species level, multivariate analysis demonstrated a statistically significant negative association between colonization with Streptococcus mitis or Lactobacillus gasseri and MRSA, and a negative association between Kocuria palustris and MRSA colonization of borderline statistical significance. Co-culture experiments revealed in vitro competition between S. mitis and all of the 22 MRSA strains isolated from subjects. Competition was blocked by addition of catalase to the media. Persistently colonized subjects had less microbial diversity than non-colonized controls.
The identification of S. mitis as a competitor to MRSA in the nasal niche via a hydrogen peroxide mechanism demonstrates that in an inpatient setting, with complex factors impacting the microbial community, interspecies competition may protect some hosts from MRSA. Furthermore, novel organisms with known mechanisms of antistaphylococcal activity, L. gasseri and K. palustris, were shown to be active against MRSA in the nasal niche.
M. T. Bessesen,
Department of Veterans Affairs:
B. Wagner, None
J. Adams, None
S. Kingery, None
J. Benoit, None
C. Robertson, None
E. Janoff, None
D. Frank, None