ABSTRACT: Mycoplasma gallisepticum (MG) can cause chronic respiratory disease (CRD) in chickens, which has a significant negative economic impact on the global poultry sector. Respiratory flora is the guardian of respiratory health, and its disorder is closely related to respiratory immunity and respiratory diseases. As a common probiotic in the chicken respiratory tract, Lactobacillus salivarius (L. salivarius) has potential antioxidant, growth performance enhancing, and anti-immunosuppressive properties. However, the specific mechanism through which L. salivarius protects against MG infection has not yet been thoroughly examined. This study intends to investigate whether L. salivarius could reduce MG-induced tracheal inflammation by modulating the respiratory microbiota and metabolites. The results indicated that L. salivarius reduced MG colonization significantly and alleviated the anomalous morphological changes by using the MG-infection model. L. salivarius also reduced the level of Th1 cell cytokines, increased the level of Th2 cell cytokines, and ameliorated immune imbalance during MG infection. In addition, L. salivarius improved the mucosal barrier, heightened immune function, and suppressed the Janus kinase/Signal transducer, and activator of transcription (JAK/STAT) signaling pathway. Notably, MG infection changed the composition of the respiratory microbiota and metabolites, and L. salivarius therapy partially reversed the aberrant respiratory microbiota and metabolite composition. Our results highlighted that these findings demonstrated that L. salivarius played a role in MG-mediated inflammatory damage and demonstrated that L. salivarius, by altering the respiratory microbiota and metabolites, could successfully prevent MG-induced inflammatory injury in chicken trachea.
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