Nakaminami Hidemasa, Ito Teruyo, Han Xiao, Ito Ayumu, Matsuo Miki, Uehara Yuki, Baba Tadashi, Hiramatsu Keiichi, Noguchi Norihisa
Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.
Department of Microbiology, Graduate School of Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo, Tokyo 113-8421, Japan.
FEMS Microbiol Lett. 2017 Sep 1;364(16). doi: 10.1093/femsle/fnx171.
SasX is a known virulence factor of Staphylococcus aureus involved in colonisation and immune evasion of the bacterium. The sasX gene, which is located on the ϕSPβ prophage, is frequently found in the sequence type (ST) 239 S. aureus lineage, which is the predominant healthcare-associated clone in Asian countries. In Japan, ST239 clones have rarely been identified, and sasX-positive strains have not been reported to date. Here, we report the first identification of 18 sasX-positive methicillin-resistant S. aureus (MRSA) strains in Japanese hospitals between 2009 and 2011. All sasX-positive isolates belonged to an ST239-staphylococcal cassette chromosome mec type III (ST239-III) lineage. However, we were unable to identify additional sasX-positive MRSA strains from 2012 to 2016, indicating that the small epidemic of sasX-positive isolates observed in this study was temporary. The sequence surrounding sasX in the strain TOHH628 lacked 51 genes that encode phage packaging and structural proteins, and no bacteriophage was induced by mitomycin C. Additionally, in the TOHH628 strain, the region (64.6 kb) containing sasX showed high identity to the ϕSPβ-like element (71.3 kb) of the Taiwanese MRSA strain Z172. The data strongly suggest that the present sasX-positive isolates found in Japanese hospitals were transmitted incidentally from other countries.
SasX是金黄色葡萄球菌已知的一种毒力因子，参与该细菌的定植和免疫逃逸。位于ϕSPβ前噬菌体上的sasX基因，在序列类型（ST）239金黄色葡萄球菌谱系中经常被发现，该谱系是亚洲国家主要的医疗保健相关克隆株。在日本，很少鉴定出ST239克隆株，迄今为止也未报告过sasX阳性菌株。在此，我们报告了2009年至2011年期间在日本医院首次鉴定出18株sasX阳性耐甲氧西林金黄色葡萄球菌（MRSA）菌株。所有sasX阳性分离株均属于ST239-葡萄球菌盒式染色体mecⅢ型（ST239-III）谱系。然而，我们在2012年至2016年期间未能鉴定出其他sasX阳性MRSA菌株，这表明本研究中观察到的sasX阳性分离株的小范围流行是暂时的。菌株TOHH628中sasX周围的序列缺少51个编码噬菌体包装和结构蛋白的基因，丝裂霉素C未诱导出噬菌体。此外，在TOHH628菌株中，包含sasX的区域（64.6 kb）与台湾MRSA菌株Z172的ϕSPβ样元件（71.3 kb）具有高度同源性。数据强烈表明，在日本医院发现的目前这些sasX阳性分离株是偶然从其他国家传播而来的。
