Low incidence of coaggregation amongst bacteria isolated from the upper respiratory tract in health and disease.

The nasal cavity harbours a commensal microbiota that reportedly provides colonization resistance against respiratory pathogens. Following the onset of chronic rhinosinusitis (CRS), a change in sinus microbiota composition is frequently reported in which atypical anaerobic and/or Gram-negative bacteria predominate. We have investigated pairwise interactions between respiratory bacteria isolated from healthy adults (n=3) and individuals exhibiting CRS (n=3). Antagonism was determined using a spot plate methodology and coaggregation scores were determined using a quantitative spectrophotometric assay. Obligate anaerobes were isolated from all CRS samples and exhibited inter-host growth inhibition of commensal nasal bacteria, including Corynebacterium spp. and Staphylococcus spp. Antagonism between bacteria isolated from healthy individuals was limited to corynebacterial-mediated inhibition of the staphylococci. The frequency of coaggregation was low overall (2/153 pairwise interactions). Antagonism of the nasal microbiota by respiratory pathogens may represent a competitive strategy in the sinus and warrants further investigation.