Chicken-derived Lactobacillus strains alleviate Mycoplasma gallisepticum infection and improve growth performance in broilers.

Restrictions on antibiotic use in poultry production have increased interest in probiotic alternatives for controlling infectious diseases. This study isolated chicken-derived Lactobacillus strains and evaluated their probiotic properties and protective effects against Mycoplasma gallisepticum (MG) infection in broilers. A total of 81 isolates were recovered from different intestinal segments of healthy chickens and assigned to four genera and six species. After screening for acid tolerance and broad-spectrum antimicrobial activity, four representative strains were selected for further study: Lactobacillus crispatus Z2, L. crispatus Z18, Ligilactobacillus agilis Z22, and Ligilactobacillus salivarius M12. In vitro, cell-free supernatants (CFS) from these strains reduced MG colony formation and significantly decreased MG adhesion to chicken alveolar epithelial type II cells (P < 0.05). At non-cytotoxic concentrations, CFS treatment also reduced mgc2 copy number and gapA expression in MG-infected cells (P < 0.05). The selected strains further showed favorable probiotic characteristics, including rapid growth, acidification capacity, and adhesion to intestinal epithelial cells. For in vivo evaluation, broilers were experimentally challenged with MG and assigned to different probiotic intervention groups, with tiamulin used as an antimicrobial control. Probiotic administration alleviated MG-associated growth impairment in broilers. Strains Z2 and Z22 significantly increased final body weight, whereas Z2, Z22, and M12 improved body weight gain during the late growth phase (P < 0.05). All four strains reduced feed conversion ratio during early growth, and Z22 also improved overall feed efficiency (P < 0.05). Histopathological analysis showed that probiotic treatment reduced inflammatory infiltration in the lung and preserved cecal epithelial integrity. TUNEL staining further demonstrated reduced pulmonary apoptosis after probiotic intervention (P < 0.05). Consistent with these effects, probiotic treatment decreased pulmonary MG burden, as reflected by lower mgc2 copy number, and downregulated the adhesion-related gene gapA in lung tissue (P < 0.05). These results support chicken-derived Lactobacillus strains as candidate antibiotic alternatives for controlling MG infection and improving broiler performance.