Zhou Wangxiao, Jin Ye, Shen Ping, Chen Weiwei, Chen Yunbo, Xiao Yonghong
State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, National Clinical Research Center for Infectious Diseases, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China.
Department of General Intensive Care Unit, The Second Affiliated Hospital of Zhejiang University School of Medicine, Hangzhou, Zhejiang, China.
J Antimicrob Chemother. 2023 Sep 5;78(9):2366-2375. doi: 10.1093/jac/dkad250.
Methicillin resistance in Staphylococcus aureus is primarily due to the mecA gene found in highly diverse staphylococcal cassette chromosome mec (SCCmec) elements, with an increasing number of variants being continually discovered.
To characterize two novel SCCmec variants identified in clonal complex (CC) 398 strains and lineage-specific pseudo-SCCmec elements in the ST88 clone.
WGS and comparative genomic analysis were used to elucidate the SCCmec element diversity of representative isolates.
The non-typeable 47 kb SCCmec found in the CC398 strain SKLX55795 represents a novel subtype of XIV, showing significant differences in structural organization and genetic content within the joining regions compared with the XIV element from the prototype strain SC792. This unique subtype comprised remnants from various mobile genetic elements that encode antimicrobial resistance genes, ultimately forming a large MDR region. Genome analysis of CC398 strain SKLX61416 revealed the presence of a novel 50 kb composite SCCmec with two distinct domains, carrying the ccr gene complexes 5/8 and containing genes for the detoxification of arsenic and sulphide. Further sequence analysis disclosed that 44.23% (23/52) of ST88 strains in our collection carried a lineage-specific pseudo-SCCmec, termed ΨSCCmecST88. This ΨSCCmecST88 harboured the mec gene complex C2, along with a series of genes associated with heavy metal resistance, but lacked an approximately 28 kb region encompassing the ccr gene complex.
Our findings provide evidence for the ongoing evolution of SCCmec elements within the CC398 and ST88 clones, underscoring the need for further surveillance to understand the biological significance of these elements.
金黄色葡萄球菌中的耐甲氧西林主要归因于在高度多样的葡萄球菌盒式染色体mec（SCCmec）元件中发现的mecA基因，并且不断有越来越多的变体被发现。
对在克隆复合体（CC）398菌株中鉴定出的两种新型SCCmec变体以及ST88克隆中的谱系特异性假SCCmec元件进行特征描述。
采用全基因组测序（WGS）和比较基因组分析来阐明代表性分离株的SCCmec元件多样性。
在CC398菌株SKLX55795中发现的不可分型的47 kb SCCmec代表了XIV型的一种新型亚型，与原型菌株SC792的XIV元件相比，其连接区域的结构组织和遗传内容存在显著差异。这种独特的亚型包含来自各种移动遗传元件的残余部分，这些元件编码抗菌抗性基因，最终形成一个大的多重耐药区域。CC398菌株SKLX61416的基因组分析揭示了一种新型的50 kb复合SCCmec的存在，该复合SCCmec具有两个不同的结构域，携带ccr基因复合体5/8，并包含用于砷和硫化物解毒的基因。进一步的序列分析表明，我们所收集的ST88菌株中有44.23%（23/52）携带一种谱系特异性假SCCmec，称为ΨSCCmecST88。这种ΨSCCmecST88包含mec基因复合体C2以及一系列与重金属抗性相关的基因，但缺少一个包含ccr基因复合体的约28 kb区域。
我们的研究结果为CC398和ST88克隆内SCCmec元件的持续进化提供了证据，强调了进一步监测以了解这些元件生物学意义的必要性。
