Institute of Veterinary Immunology & Engineering, National Research Center of Engineering and Technology for Veterinary Biologicals, Jiangsu Key Laboratory for Food Quality and Safety-State Key Laboratory Cultivation Base, Ministry of Science and Technology, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China; School of Food and Biological Engineering, Jiangsu University, Zhenjiang 212013, China; Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou 225009, China.
College of Veterinary Medicine, Nanjing Agriculture University, Nanjing, China.
Vet Microbiol. 2022 Jul;270:109450. doi: 10.1016/j.vetmic.2022.109450. Epub 2022 May 4.
Streptococcus agalactiae (S. agalactiae) causes intramammary infection in dairy cows. Increased neutrophils and a high bacterial load are important characteristics of bovine bacterial mastitis. We hypothesized that the multiplicity of infection (MOI) of S. agalactiae in bovine mastitis plays an important role in bacterial pathogenicity by modulating the neutrophil response to promote bacterial survival. Neutrophils from BALB/c mice were infected with the bovine mastitis isolate of S. agalactiae SAG-FX17 at various MOIs, and neutrophil responses were investigated. Infecting neutrophils with SAG-FX17 at an MOI of 1 induced reactive oxygen species (ROS) and neutrophil extracellular traps (NETs) formation. Bacteria at an MOI of 10 suppressed neutrophil responses, including ROS bursts, NET formation, and cell necrosis, which are conducive to bacterial multiplication within 30 min postinfection. In addition, neutrophils are destroyed by SAG-FX17 at an MOI of 100 or greater. This study identified the MOIs related to the ROS and NET suppression caused by SAG-FX17, and the findings suggested that interventions to decrease bacterial loads before the MOI of 10 could be necessary and effective to harness the power of innate immune response to eliminate pathogens.
无乳链球菌（S.agalactiae）可引起奶牛乳腺炎感染。中性粒细胞增多和高细菌负荷是牛细菌性乳腺炎的重要特征。我们假设无乳链球菌在牛乳腺炎中的感染倍数（MOI）通过调节中性粒细胞反应来促进细菌存活，从而在细菌致病性中起重要作用。用不同 MOI 的牛乳腺炎分离株 S.agalactiae SAG-FX17 感染 BALB/c 小鼠的中性粒细胞，研究中性粒细胞反应。用 MOI 为 1 的 SAG-FX17 感染中性粒细胞可诱导活性氧（ROS）和中性粒细胞胞外诱捕网（NETs）的形成。MOI 为 10 的细菌抑制中性粒细胞反应，包括 ROS 爆发、NET 形成和细胞坏死，这有利于细菌在感染后 30 分钟内增殖。此外，MOI 为 100 或更高的 SAG-FX17 可破坏中性粒细胞。本研究确定了与 SAG-FX17 引起的 ROS 和 NET 抑制相关的 MOIs，研究结果表明，在 MOI 达到 10 之前减少细菌负荷的干预措施可能是必要和有效的，可以利用先天免疫反应的力量来消除病原体。
