Potential transfer of orally administered probiotics to the upper respiratory tract in children with otitis media with effusion.

The upper respiratory tract (URT) microbiome is increasingly recognised as a key determinant of airway health, yet the potential of probiotics to beneficially modulate these communities remains largely unexplored, despite the high burden of URT infections such as otitis media (OM). This randomised controlled trial investigated the migration of two model probiotic strains, Lacticaseibacillus rhamnosus GG and Bifidobacterium animalis subsp. lactis BB-12, to different URT niches in 37 children with otitis media with effusion (OME) treated daily with oral oil drops for one month. URT samples from the adenoids, and nasopharynx were analysed with species-specific qRT-PCR and 16S amplicon sequencing. L. rhamnosus GG-like bacteria were detected in 4/19 of treated patients compared to 0/18 in the control group. Probiotic treatment with oral oil droplets modestly increased the prevalence of L. rhamnosus GG-like bacteria in the nasopharynx and adenoids (from 0% to 16.67% and 15.79% respectively), and a slight positive association was observed with the abundance of Dolosigranulum pigrum (effect size = 0.13). Interestingly, other factors, such as maternal antibiotic use after birth, were associated with a notable higher abundance of Moraxella catarrhalis/nonliquefaciens (Maaslin effect size = 5.10), and a lower abundance of Streptococcus pneumoniae/pseudopneumoniae (Maaslin effect size = -2.27). In conclusion, this study suggests that oral probiotics might modulate the URT microbiome in ways relevant to OM, although the magnitude and direction of effects likely depend on the specific strains used. The trial was registered at ClinicalTrials.gov under B300201731908.