Objectives: To investigate the protective effect of the probiotic bacterium Streptococcus salivarius K12 (K12) against Mycoplasma pneumoniae (Mp) infection in mice.
Methods: Forty male BALB/c mice were randomized into normal control group, K12 treatment group, Mp infection group, and K12 pretreatment prior to Mp infection group. The probiotic K12 was administered daily by gavage for 14 days before Mp infection induced by intranasal instillation of Mp. Three days after Mp infection, the mice were euthanized for analysis of bronchoalveolar lavage fluid (BALF) cell counts and serum levels of secretory immunoglobulin A (sIgA), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6). RT-qPCR was performed to detect the P1 and community-acquired respiratory distress syndrome ( CARDS ) toxin of Mp in the lung tissues and the mRNA expressions of TNF-α, IL-6, chemokine 1 (CXCL1), matrix metalloproteinase 9 (MMP9), mucin 5ac (MUC5ac), collagen 3a1 (Col3a1), Toll-like receptor 2 (TLR2) and TLR4; the protein expressions of TLR2 and TLR4 in the lung tissue were detected using Western blotting. Pathological changes in the lung tissue and airway remodeling were examined with HE staining and AB/PAS staining.
Results: Compared with the Mp-infected mice with PBS treatment, the infected mice with K12 treatment showed significantly lowered mRNA levels of P1 and CARDS in the lung tissue and reduced white blood cell counts in the BALF (P<0.05). In spite of the absence of significant differences in serum levels of inflammatory factors between the two groups, the mRNA expressions of TNF‑α, IL-6, CXCL1, MMP9, MUC5ac and COL3A1 and the mRNA and protein levels of TLR2 and TLR4 in the lung tissues were significantly lower in K12-treated mice, in which AB/PAS staining showed obviously decreased mucus secretion.
Conclusions: K12 pretreatment can effectively reduce pulmonary inflammatory responses, improve airway remodeling and alleviate lung injury in Mp-infected mice.
目的: 探讨唾液链球菌K12对肺炎支原体（Mp）感染小鼠是否具有预防作用。方法: 20只雄性BALB/c小鼠随机分为：正常对照组、单纯益生菌组（K12+PBS组）、单纯Mp感染组（PBS+Mp组）、益生菌预防组（K12+Mp组），5只/组。Mp感染3 d后进行支气管肺泡灌洗液（BALF）计数；ELISA检测血清中分泌型免疫球蛋白A（sIgA）、肿瘤坏死因子-α（TNF-α）和白细胞介素-6（IL-6）的表达；RT-qPCR检测肺组织中Mp的P1和社区获得性呼吸窘迫综合征（CARDS）毒素，肺组织炎症因子TNF-α、IL-6、趋化因子1（CXCL1）、肺部重塑功能基质金属酶9（MMP9）、粘蛋白5ac（MUC5ac）、胶原蛋白3a1（Col3a1）、Toll样受体2（TLR2）及TLR4的mRNA表达；Western blotting检测肺组织中TLR2和TLR4蛋白水平变化；HE染色和AB/PAS染色观察肺组织病理变化和肺部气道重塑变化。结果: K12+Mp组的P1、CARDS mRNA表达和BALF中白细胞数量较PBS+Mp组相比降低（P<0.05）。K12+Mp组血清中的炎症因子差异无统计学意义；但是肺组织中TNF-α（P<0.001）、IL-6（P<0.01）和CXCL1（P<0.05）的mRNA表达都呈下降趋势，且TLR2（P<0.01）和TLR4（P<0.001）的表达也降低。K12+Mp 组肺组织中MMP9（P<0.001）、MUC5ac （P<0.001）和COL3A1（P<0.0001）的mRNA表达呈现下降的趋势，AB/PAS 染色显示粘液分泌降低。结论: K12益生菌在一定浓度和时间范围内预防给药能有效减轻Mp感染小鼠肺部炎症反应，同时能够有效改善肺组织气道重塑功能和肺部损伤，对Mp感染小鼠有一定的预防作用。.
Keywords: BALB/c mice; Mycoplasma pneumoniae; Mycoplasma pneumoniae infection model; Streptococcus salivarius K12; oral probiotics.