Mitigation of antimicrobial resistance in staphylococcal isolates from bovine milk

当今世界最大的健康挑战之一是对用于治疗感染的抗生素产生抗药性的细菌。畜牧业是加拿大预防和治疗疾病的抗生素的最大使用者。在乳制品行业，抗生素的一个主要用途是治疗主要由病原菌引起的乳房炎。其中主要致病菌为金黄色葡萄球菌(S.aureus)和次要致病菌为凝固酶阴性葡萄球菌(CNS)。金黄色葡萄球菌乳房炎的治疗因其在组织中持续存在并逃避宿主免疫反应的能力以及缺乏有效的疫苗而变得复杂。此外，葡萄球菌异常频繁地获得抗菌素耐药性，特别是对甲氧西林的耐药性，可能导致治愈率极低。在过去的10年里，我们一直在研究牛奶金黄色葡萄球菌和中枢神经系统分离株的抗生素耐药性。这项拟议的研究建立在我们不断努力和取得成功的基础上，并利用了我们与各国科学家建立的合作。我们将进行以下工作：(1)鉴定乳汁中金黄色葡萄球菌和中枢神经系统中独特的耐甲氧西林决定簇和其他抗菌素耐药(AMR)基因。这一结果将有助于监测动物的AMR，并揭示新的干预目标；(2)在循环暴露于高浓度抗生素后，发现耐受发展过程中的特定基因突变。耐药性是细菌在抗生素下生存的主要决定因素。然而，细菌也可以对抗生素治疗产生抵抗，而不会产生耐药性，这种现象被称为“耐受”。通过研究耐受性形成过程中的遗传变化，我们可以了解新的耐药性是如何产生的；以及(3)开发新型抗菌肽(AMPs)和肽核酸(PNAS)，以消除牛乳腺上皮细胞内的金黄色葡萄球菌。AMPS和PNA都是解决细菌多重耐药问题的传统抗生素的新替代品。拟议的研究在解决引起乳房炎的细菌的AMR问题方面具有高度的原创性和创新性。这项拟议的研究将有助于了解细菌性AMR的形成机制，并减少奶牛的乳房炎。此外，这项研究可能与人类健康有关，因为来自牛奶的耐甲氧西林金黄色葡萄球菌和CNS可能通过葡萄球菌物种之间的耐药基因的水平转移和人与动物之间的耐药病原体的直接传播而对人类健康构成潜在的危害。因此，这项研究对乳品生产者具有潜在的经济效益，对动物福利甚至可能对人类的健康都有好处，对解决AMR问题的政策制定以及培养高素质的人才具有社会效益。

One of today's biggest world health challenges is bacteria that are resistant to the antibiotics used to treat infections. Animal agriculture is the largest user of antibiotics in Canada to prevent and treat diseases. In the dairy industry, one major use of antibiotics is for treating mastitis, caused mainly by pathogenic bacteria. Among them, staphylococci, including Staphylococcus aureus (S. aureus) (major pathogens) and coagulase-negative staphylococcus (CNS) (minor pathogens) are important. Treatment of S. aureus mastitis has been complicated by its ability to persist in tissues and evade the host immune response and by lack of effective vaccines. In addition, unusually frequent acquisition of antimicrobial resistance among staphylococci, especially methicillin resistance, could contribute to significantly low cure rates. We have been working on antibiotic resistance of milk S. aureus and CNS isolates for the last 10 years. This proposed research builds on our continuing efforts and successes and takes advantage of our established collaboration with scientists in various countries. We will perform the following: (1) to identify unique methicillin-resistant determinants and other antimicrobial resistance (AMR) genes in S. aureus and CNS from mastitic milk. The results will contribute to the surveillance of AMR in animals and to reveal new targets for intervention; (2) to uncover specific genetic mutations during the development of tolerance after cyclic exposure to high concentrations of antibiotics. Resistance is a primary determinant in the survival of bacteria under antibiotics. However, bacteria can also become recalcitrant to antibiotic treatment, without developing resistance, a phenomenon termed "tolerance". By studying genetic changes during the development of tolerance, we can understand how new resistance is developed; and (3) to develop novel antimicrobial peptides (AMPs) and peptide nucleic acids (PNAs) for eliminating intracellular S. aureus in bovine mammary epithelial cells. Both AMPs and PNAs are novel alternatives to traditional antibiotics to tackle the problem of bacterial multidrug resistance. The proposed research is highly original and innovative for solving the AMR problem in mastitis-causing bacteria. This proposed research will contribute to understanding mechanisms for the formation of bacterial AMRs and to reduce mastitis in dairy cows. In addition, this research may be relevant to human health because methicillin-resistant S. aureus and CNS from milk potentially pose a hazard to human health, both through horizontal transfer of resistance genes between staphylococcal species and through direct transmission of resistant pathogens between humans and animals. Therefore, this proposed research has potential economic benefits to dairy producers, health benefits to animal welfare and possibly to humans, and social benefits to policy making for dealing with the AMR problem as well as training highly qualified personnel.