What gets up your nose?

Nostrils Staphylococcus aureus is an invasive human pathogen with increasing incidence and morbidity in hospitals and the community. Both healthy persons and those with underlying illness are at risk for diverse skin and soft tissue infections, endocarditis, osteomyelitis, meningitis, bacteremia, and pneumonia (including pneumonia arising as a complication of influenza), with mortality rates ranging from 6–40%. The high frequency of poorly responsive and recurrent S. aureus disease in apparently immunocompetent hosts is a challenging feature of these infections. Groups that are particularly susceptible include children in daycare, sports teams, jailed inmates and military personnel. Moreover, the emergence and rapid spread of methicillin-resistant S. aureus (MRSA) has placed substantial burden on the healthcare system.

Colonization of the nares (nostrils) is a potent and increasingly prevalent risk factor for subsequent S. aureus infection. In at least 80% of S. aureus bacteremia cases in colonized subjects, the infecting strain is identical to a nasal colonizing strain detected prior to onset of bacteremia. Followed longitudinally, approximately 20–30% of persons are colonized persistently with S. aureus, 30% are colonized intermittently, and 50% never, or rarely, are colonized. Why some individuals apparently are resistant to colonization, and thus at lower risk of infection, remains an open question. Understanding the biology of this pathogen, especially its ecological niche in humans and the initial step in infection, colonization, may therefore provide new methods of limiting disease.

The Human Nasal Microbiota and Staphylococcus aureus Carriage. 2010 PLoS ONE 5(5): e10598. doi:10.1371/journal.pone.0010598
Nasal specimens were collected longitudinally from five healthy adults and a cross-section of hospitalized patients (26 S. aureus carriers and 16 non-carriers). Culture-independent analysis of 16S rRNA sequences revealed that the nasal microbiota of healthy subjects consists primarily of members of the phylum Actinobacteria (e.g., Propionibacterium spp. and Corynebacterium spp.), with proportionally less representation of other phyla, including Firmicutes (e.g., Staphylococcus spp.) and Proteobacteria (e.g. Enterobacter spp). In contrast, inpatient nasal microbiotas were enriched in S. aureus or Staphylococcus epidermidis and diminished in several actinobacterial groups, most notably Propionibacterium acnes. Moreover, within the inpatient population S. aureus colonization was negatively correlated with the abundances of several microbial groups, including S. epidermidis. The nares environment is colonized by a temporally stable microbiota that is distinct from other regions of the integument. Negative association between S. aureus, S. epidermidis, and other groups suggests microbial competition during colonization of the nares, a finding that could be exploited to limit S. aureus colonization.

