Abstract
Under eubiotic conditions commensal microbes are known to provide a competitive barrier against invading bacterial pathogens in the intestinal tract, on the skin or on the vaginal mucosa. Here, we evaluate the role of lung microbiota in Pneumococcus colonization of the lungs. In eubiosis, the lungs of mice were dominantly colonized by Lactobacillus murinus. Differential analysis of 16S rRNA gene sequencing or L. murinus-specific qPCR of DNA from total organ homogenates vs.broncho alveolar lavages implicated tight association of these bacteria with the host tissue. Pure L. murinus conditioned culture medium inhibited growth and reduced the extension of pneumococcal chains. Growth inhibition in vitro was likely dependent on L. murinus-produced lactic acid, since pH neutralization of the conditioned medium aborted the antibacterial effect. Finally, we demonstrate that L. murinus provides a barrier against pneumococcal colonization in a respiratory dysbiosis model after an influenza A virus infection, when added therapeutically.
Highlights
Mucosal surfaces are major entry ports for microbial pathogens
We previously demonstrated dominance of Lactobacillaceae in total lower respiratory tract (LRT)
In order to characterize these Lactobacillaceae in greater detail, we independently isolated and characterized two clones of phenotypically dominant bacteria from LRT homogenates cultivated on Columbia agar plates
Summary
In the densely colonized gut, commensal bacteria confer a prominent protective role against invading bacterial pathogens, in part by posing a competitive threshold within this ecological niche (Barthel et al, 2003). This biological barrier is absent in axenic mice and reduced in mice harboring a low-complexity microbiota colonized mice. Skin microbiota poses a similar barrier against colonization by bacterial skin pathogens (reviewed in Parlet et al., 2019). It became evident that the lower respiratory tract (LRT), previously considered quasi-sterile, hosts a bacterial microbiota under healthy conditions (Dickson et al, 2015)
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