Differential responses of human dendritic cells to metabolites from the oral/airway microbiome.

Small molecule metabolites that are produced or altered by host-associated microbial communities are emerging as significant immune response modifiers. However, there is a key gap in our knowledge of how oral microbial metabolites affect the immune response. Here, we examined the effects of metabolites from five bacterial strains found commonly in the oral/airway microbial communities of humans. The five strains, each isolated from cystic fibrosis patient sputum, were Pseudomonas aeruginosa FLR01 non-mucoid (P1) and FLR02 mucoid (P2) forms, Streptococcus pneumoniae (Sp), S. salivarius (Ss) and Rothia mucilaginosa (Rm). The effect of bacterial metabolites on dendritic cell (DC) activation, T cell priming and cytokine secretion was determined by exposing DCs to bacterial supernatants and individual metabolites of interest. Supernatants from P1 and P2 induced high levels of tumour necrosis factor (TNF)-α, interleukin (IL)-12 and IL-6 from DCs and primed T cells to secrete interferon (IFN)-γ, IL-22 compared to supernatants from Sp, Ss and Rm. Investigations into the composition of supernatants using gas chromatography-mass spectroscopy (GC-MS) revealed signature metabolites for each of the strains. Supernatants from P1 and P2 contained high levels of putrescine and glucose, while Sp and Ss contained high levels of 2,3-butanediol. The individual metabolites replicated the results of whole supernatants, although the magnitudes of their effects were reduced significantly. Altogether, our data demonstrate for the first time that the signature metabolites produced by different bacteria have different effects on DC functions. The identification of signature metabolites and their effects on the host immune system can provide mechanistic insights into diseases and may also be developed as biomarkers.

Effects of amoxicillin treatment on the salivary microbiota in children with acute otitis media.

Amoxicillin is a first-line antibiotic treatment for acute otitis media in children and one of the most commonly used antibiotics for human bacterial infections. We investigated changes in salivary bacterial communities among children treated with amoxicillin for acute otitis media (n = 18), using a culture-independent approach based on pyrosequencing of the V3 region of the bacterial 16S rRNA gene. The control group consisted of children with acute otitis media who were not given antibiotics (n = 15). One species-level phylotype assigned to the genus Streptococcus was identified across all (n = 99) saliva samples. Two additional species-level phylotypes from the genera Gemella and Granulicatella were shared by all (n = 45) samples of control subjects. Amoxicillin treatment resulted in reduced species richness and diversity, and a significant shift in the relative abundance of 35 taxa at different ranks from phylum to species-level phylotype. At the phylum level, prevalence of TM7 and Actinobacteria decreased at the end of treatment, whereas Proteobacteria had a higher relative abundance post-treatment. Multivariate analysis showed that samples from the same control subject taken over time intervals tended to cluster together. Among antibiotic-treated subjects, samples taken before and at the end of amoxicillin treatment formed two relatively well-separated clusters both of which greatly overlapped with samples taken about 3 weeks post-treatment. Our results point to a substantial but incomplete recovery of the salivary bacterial community from the antibiotic about 3 weeks after the end of treatment.