Commensal microbiota has been shown to play an important role in local infections. However, the correlation between host respiratory microbiota and Mycoplasma gallisepticum (MG) infection is not well characterized. Here, the results of 16S rRNA sequencing showed that MG infection correlated with alteration in respiratory microbiota of chickens characterized by decreased richness and diversity. To explore whether respiratory microbiota contributed to MG infection, an antibiotics cocktail was used to deplete respiratory microbiota. It has been found that depletion of respiratory Gram-positive and Gram-negative bacteria promoted MG infection, as reflected in the form of increased MG colonization, pro-inflammatory cytokines and proteins expression, and severe lung damage compared to the control group. Importantly, depletion of Gram-negative bacteria in respiratory tract mitigated MG infection, which indicated that certain Gram-negative bacteria may promote MG infection. By reconstitution of individual cultivable respiratory tract bacteria in antibiotic-treated chickens, a respiratory commensal microbe Serratia marcescens was identified to facilitate MG infection. We further found that Serratia marcescens may promote MG infection by downregulating Mucin 2 (MUC2) and tight junction related gene mRNA expression levels in trachea and lung tissues. Together, our data demonstrated that MG infection induced disturbed respiratory microbiota and the specific respiratory commensal bacterium Serratia marcescens could promote MG infection, and thus expand our understanding of the pathogenesis of MG infection.

共生菌群已显示在局部感染中起重要作用。然而，宿主呼吸菌群和鸡支原体之间的相关性（MG）感染没有很好的特征。在这里，16S rRNA测序的结果表明，MG感染与以丰富度和多样性下降为特征的鸡呼吸菌群变化有关。为了探讨呼吸菌群是否导致MG感染，使用了一种抗生素混合物来消耗呼吸菌群。现已发现，与对照组相比，呼吸道革兰氏阳性和革兰氏阴性细菌的耗竭促进了MG感染，表现为MG定植增加，促炎性细胞因子和蛋白质表达以及严重的肺损伤。重要的是，呼吸道革兰氏阴性菌的消耗减轻了MG的感染，这表明某些革兰氏阴性菌可能会促进MG的感染。已鉴定出粘质沙雷氏菌有助于MG感染。我们进一步发现粘质沙雷氏菌可能通过下调气管和肺组织中的粘蛋白2（MUC2）和紧密连接相关基因mRNA表达水平来促进MG感染。总之，我们的数据表明，MG感染可引起呼吸道微生物菌群紊乱，而特定的呼吸共生细菌粘质沙雷氏菌可促进MG感染，从而加深了我们对MG感染发病机理的了解。