Faculty of Science, Cochin University of Science and Technology, Cochin-682022, India.
Microbiology Fermentation and Biotechnology (MFB) Division, ICAR- Central Institute of Fisheries Technology (ICAR-CIFT), Matsyapuri P.O., Willingdon, Cochin 682029, India.
BMC Microbiol. 2024 Sep 10;24(1):334. doi: 10.1186/s12866-024-03469-0.
Characteristics of non-clinical strains of methicillin-resistant Staphylococcus aureus (MRSA) especially from fishery environment are poorly understood. This research, in addition to comprehensive characterisation, sought to delineate the genetic relatedness between the MRSA strains originating from clinical as well as non-clinical settings. Out of 39 methicillin-resistant staphylococcal isolates from 197 fish samples, 6 (Three each of methicillin-resistant S. haemolyticus (MRSH) and MRSA) with distinct resistance profiles were selected for whole-genome sequencing. Using respective bioinformatics tools, MRSA genomes were comprehensively characterized for resistome, virulomes, molecular epidemiology and phylogenetic analysis. Simultaneously, MRSH genomes were specifically examined to characterize antimicrobial resistance genes (ARGs), owing to the fact that MRSH is often recognized as a reservoir for resistance determinants.
Three MRSA clones identified in this study include ST672-IVd/t13599 (sequence type-SCCmec type/spa type), ST88-V/t2526, and ST672-IVa/t1309. Though, the isolates were phenotypically vancomycin-sensitive, five of the six genomes carried vancomycin resistance genes including the VanT (VanG cluster) or VanY (VanM cluster). Among the three MRSA, only one harbored the gene encoding Panton-Valentine Leukocidin (PVL) toxin, while staphylococcal enterotoxin (SEs) genes such as sea and seb, associated with staphylococcal food poisoning were identified in two other MRSA. Genomes of MRSH carried a composite of type V staphylococcal cassette chromosome mec (SCCmec) elements (5C2 & 5). This finding may be explained by the inversion and recombination events that may facilitate the integration of type V elements to the SCC elements of S. aureus with a methicillin-susceptible phenotype. Phylogenetically, MRSA from a non-clinical setting displayed a considerable relatedness to that from clinical settings.
This study highlights the genetic diversity and resistance profiles of MRSA and MRSH, with non-clinical MRSA showing notable relatedness to clinical strains. Future research should explore resistance gene transfer mechanisms and environmental reservoirs to better manage MRSA spread.
耐甲氧西林金黄色葡萄球菌（MRSA）的非临床菌株的特征，特别是来自渔业环境的特征，了解甚少。这项研究除了全面描述外，还试图描绘来自临床和非临床环境的 MRSA 菌株之间的遗传关系。在 197 个鱼样中分离出 39 株耐甲氧西林葡萄球菌，其中 6 株（耐甲氧西林溶血葡萄球菌（MRSH）和 MRSA 各 3 株）具有不同的耐药谱，被选择进行全基因组测序。使用各自的生物信息学工具，全面描述了 MRSA 基因组的耐药组、毒力组、分子流行病学和系统发育分析。同时，由于 MRSH 通常被认为是耐药决定因素的储库，专门检查了 MRSH 基因组以确定抗菌药物耐药基因（ARGs）。
本研究鉴定的 3 个 MRSA 克隆包括 ST672-IVd/t13599（序列类型-SCCmec 类型/ spa 类型）、ST88-V/t2526 和 ST672-IVa/t1309。尽管这些分离株表型上对万古霉素敏感，但其中 6 个基因组中有 5 个携带万古霉素耐药基因，包括 VanT（VanG 簇）或 VanY（VanM 簇）。在这 3 株 MRSA 中，只有一株携带编码杀白细胞素（PVL）毒素的基因，而另 2 株则携带与葡萄球菌食物中毒有关的葡萄球菌肠毒素（SEs）基因，如 sea 和 seb。MRSH 基因组携带类型 V 葡萄球菌盒式染色体 mec（SCCmec）元件（5C2 和 5）的组合。这一发现可能是由于反转和重组事件，这些事件可能促进了具有甲氧西林敏感表型的金黄色葡萄球菌的 SCC 元件与类型 V 元件的整合。系统发育分析表明，来自非临床环境的 MRSA 与来自临床环境的 MRSA 具有相当大的亲缘关系。
本研究强调了 MRSA 和 MRSH 的遗传多样性和耐药谱，非临床 MRSA 与临床菌株具有显著的亲缘关系。未来的研究应探索耐药基因转移机制和环境储库，以更好地管理 MRSA 的传播。
