Respiratory microbiota dynamics following Streptococcus pneumoniae acquisition in young and elderly mice

The upper respiratory tract (URT) is a distinct microbial niche of low-density bacterial communities and, also, a portal of entry for many potential pathogens, including Streptococcus pneumoniae. Thus far, animal models have been used to study the dynamics of and interactions between limited numbers of different species in the URT. Here, we applied a deep sequencing approach to explore, for the first time, the impact of S. pneumoniae acquisition on URT microbiota in a mouse model, as well as potential age-dependent effects. Young-adult and elderly mice were inoculated intranasally with S. pneumoniae, and nasal lavage samples were collected for up to 28 days postcolonization. Bacterial DNA extracted from lavage samples was subjected to barcoded pyrosequencing of the V5-to-V7 hypervariable region of the small-subunit rRNA gene. We observed highly diverse microbial profiles, with the presence overall of 15 phyla and approximately 645 operational taxonomic units (OTUs). We noted differences in the composition of microbiota between young and elderly mice, with a significantly higher abundance of Bacteroidetes in the young mice. The introduction of S. pneumoniae into the URT led to a temporary dominance of pneumococci in the microbiota of all mice, accompanied by a significant decrease in microbial diversity. As mice gradually cleared the colonization, the diversity returned to baseline levels. Diversification was accompanied by an early expansion of Bacteroidetes, Staphylococcus spp., and Lachnospiraceae. Moreover, the Bacteroidetes expansion was significantly greater in young-adult than in elderly mice. In conclusion, we observed differences in URT microbiota composition between naive young-adult and elderly mice that were associated with differences in pneumococcal clearance over time.