Nasal microbiota and symptom persistence in acute respiratory tract infections in infants

Neumann, Roland P.; Hilty, Markus; Xu, Binbin; Usemann, Jakob; Korten, Insa; Mika, Moana; Müller, Loretta; Latzin, Philipp; Frey, Urs

Viral-bacterial interactions are complex and certain combinations of viruses and bacteria can exert either synergistic or inhibitory effects. It seems that certain bacteria can lead to an enhanced or reduced inflammatory response, and thereby modulate the burden of respiratory symptoms [8] . In clusters of infants with persistent symptoms 3 weeks after the onset of infection the microbiota was dominated by Moraxellaceae and Streptococcaceae. A higher abundance of these two potentially pathogenic bacterial families might result in an ARI with sustained symptoms. This is in accordance with a recent study of young children showing an exaggerated inflammatory response to RSV in the presence of nasopharyngeal microbiota enriched with H. influenzae and S. pneumoniae [8] . In contrast, in cluster B2, in which infants had fewer symptoms, the microbiota contained higher abundances of Corynebacteriaceae and Staphylococcaceae. These organisms have similarly been identified by TEO et al. [5] to be associated with respiratory health [19] . Nasopharyngeal Staphylococcus aureus was found to be associated with lower disease severity in RSV infections [8] . BIESBROEK et al. [23] and BOSCH et al. [19] reported less ARI in infants with nasopharyngeal microbiota dominated by Corynebacterium and Dolosigranulum. Whether these organisms are simply biomarkers indicating respiratory health, or whether they have immediate protective effects on the respiratory tract, remains unclear. Cluster B2 was also characterised by higher bacterial diversity compared to the other clusters. Lower diversity in infants with longer persistence of symptoms could reflect an outgrowth of certain potentially pathogenic bacterial families, e.g. Moraxellaceae, or potentially a lack of beneficial microbiota. It has been shown that the production of pro-inflammatory cytokines by dendritic cells is higher after stimulation by M. catarrhalis and H. influenzae compared to Prevotella strains, common commensals of the respiratory tract microbiota. Co-stimulation with Prevotella reduces the H. influenzae-induced production of pro-inflammatory cytokines [25] . This could indicate that commensals, such as Prevotella and others, are not only filling a niche, but are also functionally important for the maintenance of "healthy" equilibrium. In a recent study, we observed that a lower bacterial diversity was associated with more frequent HRV infections in the first year of life [26] .