Control of Klebsiella pneumoniae pulmonary infection and immunomodulation by oral treatment with the commensal probiotic Bifidobacterium longum 51A

Klebsiella pneumoniae (Kp) a common cause of pneumonia leads to intense lung injury and mortality that are correlated with infective exacerbations. Probiotics are a class of microorganisms that have immunomodulatory effects to benefit health. We investigated whether the probiotic Bifidobacterium longum 51A induces protection in mice against lung infection induced by Kp and the potential involved mechanisms. Kp infection induced secretion of pro-inflammatory cytokines, neutrophil recruitment, significant bacterial load in the lung and 50% lethality. However, treatment with live B. longum 51A induced faster resolution of inflammation associated with an increased production of IL-10, decreased lung damage with significantly reduction of bacterial burden that contributed to rescue 100% of mice from death. We found that these effects could be attributed, at least in part, to activation of the Toll-like receptor (TLR) adapter protein Mal, since B. longum 51A treatment in Mal-deficient infected mice did not show the protection observed in wild type infected mice. Thus, we propose that live B. longum 51A activates TLR-signaling pathway that results in ROS production and protects the host against pneumonia-induced death by finely tuning the inflammatory response and contributing to faster return to lung homeostasis.