生鲜蔬菜来源的蜡样芽胞杆菌毒力基因分布与MLST分析

MLST analysis and distribution of virulence genes of Bacillus cereus from vegetables in Shanghai

为了解生鲜蔬菜来源蜡样芽胞杆菌的分子流行病学特征,采用PCR技术对来自5种生鲜蔬菜的37株蜡样芽胞杆菌分离株进行了毒力基因(nheA、nheB、nheC、hblA、hblC、hblD、entFM、cytK、ces)检测和多位点序列分型(MLST)分析。结果表明:37株分离株除呕吐毒素基因ces未检出外,其他8个毒力基因均有检出,其中溶血性肠毒素基因nheB的检出率最高,为94.6%,其次为溶血素基因hblC、hblD、hblA和肠毒素基因entFM,检出率均超过80%,溶血性肠毒素基因nheA和nheC检出率较低,分别为78.4%和64.9%;细胞毒素基因cytK的检出率最低,为29.7%。根据毒力基因携带模式,将37株分离菌株分成14个型别,II型携带率最高,携带Hbl和Nhe两种基因的型别有I型、II型和IV型。MLST分析则发现,37株分离菌株可分为30个ST型和5个CC群。ST4和ST378为主要ST型;CC142分布最广泛,不仅包含的ST型最多,而且携带5种毒力型别。以上结果表明,上海市蔬菜中蜡样芽胞杆菌具有潜在肠毒性危害并在遗传上呈现出多样性。该结果对蔬菜中蜡样芽胞杆菌引起食物的监控、预警和爆发后感染源追踪具有指导意义。

To study the virulence gene distribution and the subtype of Bacillus cereus derived from vegetables in Shanghai,37 Bacillus cereus strains isolated from cucumber,lettuce,coriander,chicory,and sprouts were characterized.The results showed that 8 virulence genes(nheA,nheB,nheC,hblA,hblC,hblD,entFM,cytK)were detected in all the isolates except ces.The highest detection rate of virulence genes was nheB,followed by hblC,hblD,entFM,and hblA,with detection rates exceeded 80%.The detection rates of nheA and nheC were 78.4%and 64.9%,respectively,while cytK got the lowest rate(29.73%).According to the virulence gene carrying mode,37 isolated strains were divided into 14 types,among which type II carried the highest rate.Type I,type II,and type IV carried both Hbl and Nhe genes.In addition,MLST typing results showed that there were 30 STs and 5 CC groups in 37 isolated strains,ST4 and ST378 were the main STs.CC142 was distributed widely,it not only contained the most STs but also carried 5 virulence types.The distribution of virulence genes in STs was diverse.The above results indicated that Bacillus cereus in vegetables in Shanghai had potential enterotoxin hazards and presented genetic diversity,which had significant implications for monitoring,early warning,and tracking of the source of infection after outbreaks of food poisoning caused by Bacillus cereus.