Identification of factors that led to the development of pig-associated epidemic MRSA clone

自2000年代中期以来，在德国、中国和世界其他地区的猪中发现了家畜相关的耐甲氧西林金黄色葡萄球菌（LA-MRSA）分离株。在猪中，LA-MRSA分离株通常作为定植体出现；由它们引起的疾病很少见到。通过多位点序列分型对LA-MRSA分离株进行分子分析，发现中国的LA-MRSA优势克隆属于克隆复合体（CC） 9，而世界其他地区的LA-MRSA优势克隆属于CC398。造成这种差异的原因尚不清楚。拟议项目的目的是找出导致与猪相关的MRSA克隆流行病发展的因素。为此，我们提出了一种合作方法，包括对(i)流行病学上成功从中国定殖的LA-MRSA CC9和来自德国的不成功的同类，以及（ii）流行病学上成功从德国定殖的LA-MRSA CC398和来自中国的不成功的同类进行全面和比较分析。全基因组测序和核心基因组和辅助基因组的详细分析将提供属于同一CC的成功和未成功定植菌的遗传组成的详细信息。将分析在成功定植的分离株中存在而在未成功定植的分离株中缺失的基因，以确定其在毒力、粘附性、存活或调节过程中的作用。此外，将研究这四组分离物的代谢特性、适应性、存活率、与上皮细胞的粘附性、生物膜形成能力和生长特性。特别是，我们想确定在体外和体内条件下，成功的定植体是否比不成功的定植体更具竞争力，以及成功的定植体如何改变鼻腔微生物群。转录组研究将揭示不同的LA-MRSA CC9和CC398分离株在定植猪前鼻孔后的基因上调和下调。最后，将研究LA-MRSA CC398和CC9克隆的scmec卡带在甲氧西林敏感金黄色葡萄球菌（MSSA）中的可转移性，以深入了解新MRSA克隆的兴起。预期的结果将为导致MRSA克隆流行的因素提供重要的基础信息。这将有助于设计预防和干预措施，使猪（也可能是其他食品生产动物）免于感染LA-MRSA。

Since the mid-2000s, livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) isolates have been identified among pigs in Germany, China and in various other parts of the world. In pigs, LA-MRSA isolates usually occur as colonizers; diseases caused by them are rarely seen. Molecular analysis of the LA-MRSA isolates by multi-locus sequence typing identified the dominant clones of LA-MRSA in China to belong to the clonal complex (CC) 9, whereas the dominant LA-MRSA clones in the rest of the world were assigned to CC398. The reason for this difference is unknown. The aim of the proposed project is to find out the factors that led to the development of a pig-associated epidemic MRSA clone. For this, we propose a collaborative approach including a comprehensive and comparative analysis of (i) the epidemiologically successful colonizing LA-MRSA CC9 from China and their non-successful counterparts from Germany but also (ii) the epidemiologically successful colonizing LA-MRSA CC398 from Germany and their non-successful counterparts from China. Whole genome sequencing and detailed analysis of the core genome and the accessory genome will provide details about the genetic composition of the successful versus non-successful colonizers belonging to the same CC. Genes present in the successfully colonizing isolates but absent in the non-successfully colonizing isolates will be analysed for their role in virulence, adherence, survival or regulatory processes. Moreover, all four groups of isolates will be investigated for their metabolic properties, fitness, survival rates, adhesion to epithelial cells, capacity of biofilm formation, and growth characteristics. In particular, we want to determine whether (or not) the successful colonizers outcompete the non-successful colonizers under in-vitro and in-vivo conditions and how colonization with a successful colonizer changes the nasal microbiome. Transcriptome studies will reveal the genes of different LA-MRSA CC9 and CC398 isolates that are up- and down-regulated after having colonized the porcine anterior nares. Finally, the transferability of SCCmec cassettes from LA-MRSA CC398 and CC9 clones into methicillin-susceptible S. aureus (MSSA) will be investigated to gain insight into the rise of new MRSA clones. The anticipated results will provide important basic information regarding the factors that led to the development of epidemic MRSA clones. This will help to design prevention and intervention measures to keep pigs (and possibly also other food-producing animals) free of LA-MRSA.