Lactic Acid Bacteria Isolated from Bovine Mammary Microbiota: Potential Allies against Bovine Mastitis

Bovine mastitis is a costly disease in dairy cattle worldwide. As of yet, the control of bovine mastitis is mostly based on prevention by thorough hygienic procedures during milking. Additional strategies include vaccination and utilization of antibiotics. Despite these measures, mastitis is not fully under control, thus prompting the need for alternative strategies. The goal of this study was to isolate autochthonous lactic acid bacteria (LAB) from bovine mammary microbiota that exhibit beneficial properties that could be used for mastitis prevention and/or treatment. Sampling of the teat canal led to the isolation of 165 isolates, among which a selection of ten non-redundant LAB strains belonging to the genera Lactobacillus and Lactococcus were further characterized with regard to several properties: surface properties (hydrophobicity, autoaggregation); inhibition potential of three main mastitis pathogens, Staphylococcus aureus, Escherichia coli and Streptococcus uberis; colonization capacities of bovine mammary epithelial cells (bMEC); and immunomodulation properties. Three strains, Lactobacillus brevis 1595 and 1597 and Lactobacillus plantarum 1610, showed high colonization capacities and a medium surface hydrophobicity. These strains are good candidates to compete with pathogens for mammary gland colonization. Moreover, nine strains exhibited anti-inflammatory properties, as illustrated by the lower IL-8 secretion by E. coli-stimulated bMEC in the presence of these LAB. Full genome sequencing of five candidate strains allowed to check for undesirable genetic elements such as antibiotic resistance genes and to identify potential bacterial determinants involved in the beneficial properties. This large screening of beneficial properties while checking for undesirable genetic markers allowed the selection of promising candidate LAB strains from bovine mammary microbiota for the prevention and/or treatment of bovine mastitis.牛乳腺炎（Bovine mastitis）是全球范围内给奶牛养殖业造成重大经济损失的疾病。截至目前，牛乳腺炎的防控主要依靠挤奶过程中严格的卫生操作流程开展预防，其他防控策略还包括疫苗接种与抗生素的使用。尽管采取了上述措施，牛乳腺炎仍无法得到完全控制，因此亟需开发替代防控方案。本研究的目标是从牛乳房菌群中分离具有有益特性的本土乳酸菌（LAB），以期将其用于牛乳腺炎的预防和/或治疗。通过对乳头管进行采样，本研究共分离得到165株菌株，其中选取10株属于乳杆菌属（Lactobacillus）和乳球菌属（Lactococcus）的非冗余LAB菌株，针对多项特性展开进一步表征：包括表面特性（疏水性、自凝集性）；对三种主要牛乳腺炎致病菌——金黄色葡萄球菌（Staphylococcus aureus）、大肠埃希氏菌（Escherichia coli）和乳房链球菌（Streptococcus uberis）的抑制潜力；牛乳腺上皮细胞（bMEC）定植能力；以及免疫调节特性。其中短乳杆菌（Lactobacillus brevis）1595、1597以及植物乳杆菌（Lactobacillus plantarum）1610这三株菌株表现出较强的定植能力与中等水平的表面疏水性，此类菌株可作为竞争乳腺定植位点以抑制致病菌的优质候选菌株。此外，9株菌株展现出抗炎特性，具体表现为：当这些LAB与大肠埃希菌共刺激牛乳腺上皮细胞（bMEC）时，后者分泌的白细胞介素8（IL-8）水平显著降低。对5株候选菌株进行全基因组测序后，可排查其是否携带抗生素抗性基因等不良遗传元件，并鉴定出与有益特性相关的潜在细菌决定因子。本研究通过对有益特性进行大规模筛选，同时结合不良遗传标记的排查，最终从牛乳房菌群中筛选出具备应用前景的LAB候选菌株，可用于牛乳腺炎的预防和/或治疗。