Starting primarily as an inflammation of the mammary gland, mastitis is frequently driven by infectious agents such as Staphylococcus aureus. Mastitis has a large economic impact globally, which includes diagnostic, treatment, and the production costs not to mention the potential milk contamination with antimicrobial residues. Currently, mastitis prevention and cure depends on intramammary infusion of antimicrobials, yet, their overuse risks engendering resistant pathogens, posing further threats to livestock. In our study we aimed to investigate, in vitro, using bovine mammary epithelial cells (MAC-T), the efficacy of the AuraShield an antimicrobial mixture (As) in preventing S. aureus attachment, internalisation, and inflammation. The antimicrobial mixture (As) included: 5% maltodextrin, 1% sodium chloride, 42% citric acid, 18% sodium citrate, 10% silica, 12% malic acid, 9% citrus extract and 3% olive extract (w/w). Herein we show that As can significantly reduce both adherence and invasion of MAC-T cells by S. aureus, with no impact on cell viability at all concentrations tested (0.1, 0.2, 0.5, 1%) compared with untreated controls. The anti-apoptotic effect of As was achieved by significantly reducing cellular caspase 1, 3 and 8 activities in the infected MAC-T cells. All As concentrations were proven to be subinhibitory, suggesting that Ac can reduce S. aureus virulence without bacterial killing and that the effect could be dual including a host modulation effect. In this context, we show that As can reduce the expression of S. aureus clumping factor (ClfB) and block its interaction with the host Annexin A2 (AnxA2), resulting in decreased bacterial adherence in infection of MAC-T cells. Moreover, the ability of As to block AnxA2 had a significant decreasing effect on the levels of pro inflammatory cytokine released upon S. aureus interaction with MAC-T cells. The results presented in this study indicate that mixtures of natural antimicrobials could potentially be considered an efficient alternative to antibiotics in treating S. aureus induced mastitis.

中文翻译：

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使用体外乳腺炎模型研究天然抗菌剂在预防金黄色葡萄球菌侵袭 MAC-T 细胞中的机制作用

乳腺炎最初是乳腺炎症，通常由金黄色葡萄球菌等传染源引起。乳腺炎在全球范围内产生巨大的经济影响，包括诊断、治疗和生产成本，更不用说潜在的牛奶污染抗菌剂残留物。目前，乳腺炎的预防和治疗主要依靠乳房内输注抗菌药物，但过度使用抗菌药物可能会产生耐药性病原体，对牲畜造成进一步威胁。在我们的研究中，我们旨在使用牛乳腺上皮细胞 (MAC-T) 体外研究 AuraShield 抗菌混合物 (As) 在预防金黄色葡萄球菌附着、内化和炎症方面的功效。抗菌混合物 (As) 包括：5% 麦芽糖糊精、1% 氯化钠、42% 柠檬酸、18% 柠檬酸钠、10% 二氧化硅、12% 苹果酸、9% 柑橘提取物和 3% 橄榄提取物（w/w） 。在此，我们表明，与未处理的对照相比，As 可以显着减少金黄色葡萄球菌对 MAC-T 细胞的粘附和侵袭，且在所有测试浓度（0.1、0.2、0.5、1%）下对细胞活力没有影响。As 的抗凋亡作用是通过显着降低受感染 MAC-T 细胞中的细胞 caspase 1、3 和 8 活性来实现的。所有 As 浓度均被证明是亚抑制性的，这表明 Ac 可以降低金黄色葡萄球菌的毒力而不杀死细菌，并且这种效应可能是双重的，包括宿主调节效应。在这种情况下，我们发现 As 可以降低金黄色葡萄球菌聚集因子 (ClfB) 的表达，并阻断其与宿主膜联蛋白 A2 (AnxA2) 的相互作用，从而导致 MAC-T 细胞感染时细菌粘附减少。此外，As 阻断 AnxA2 的能力对金黄色葡萄球菌与 MAC-T 细胞相互作用时释放的促炎细胞因子的水平具有显着降低作用。本研究的结果表明，天然抗菌剂的混合物可能被认为是治疗金黄色葡萄球菌引起的乳腺炎的抗生素的有效替代品。