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 5 1A 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 5 1A 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 5 1A treatment in Mal-deficient infected mice did not show the protection observed in wild type infected mice. Thus, we propose that live B. longum 5 1A 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. [ABSTRACT FROM AUTHOR]