Virulence genes in Escherichia coli isolates from commercialized saltwater mussels Mytella guyanensis (Lamarck, 1819)

Abstract The isolation of Escherichia coli from food is a major concern. Pathogenic strains of these bacteria cause diseases which range from diarrhea to hemolytic-uremic syndrome. Therefore the virulence genes in E. coli isolates from the mussel ( Mytella guyanensis) commercialized in Cachoeira, Bahia, Brazil were investigated. Samples were purchased from four vendors: two from supermarkets and two from fair outlets. They were conditioned into isothermal boxes with reusable ice and transported to the laboratory for analysis. E. coli strains were isolated in eosin methylene blue agar, preserved in brain-heart infusion medium with 15% glycerol and stored at -20 °C, after microbiological analysis. Virulence genes in the isolated strains were identified by specific primers, with Polymerase Chain Reaction. Twenty-four isolates were obtained, with a prevalence of elt gene, typical from enterotoxigenic infection, in 75% of the isolates. The stx and bfpA genes, prevalent in enterohemorragic and enteropathogenic E. coli, respectively, were not detected. The occurrence of elt virulence-related gene in the E. coli isolates of Mytella guyanensis reveals urgent improvement in food processing, including good handling practices, adequate storage and cooking before consumption, to ensure consumer’s health.

摘要 从食品中分离大肠杆菌（Escherichia coli）是备受关注的研究议题。该菌的致病菌株可引发从腹泻到溶血性尿毒综合征（hemolytic-uremic syndrome）的多种疾病。为此，本研究针对巴西巴伊亚州卡舒埃拉市商业化售卖的圭亚那紫贻贝（Mytella guyanensis）来源的大肠杆菌分离株的毒力基因展开了调查。研究样本从4家销售点采购：2家超市及2家农贸市场摊位。样本被置于搭载可重复使用冰袋的恒温箱中，运送至实验室进行分析。研究人员采用伊红美蓝琼脂（eosin methylene blue agar）培养基分离大肠杆菌菌株，将其保存在含15%甘油的脑心浸液培养基（brain-heart infusion medium）中，并于-20℃条件下储存，随后完成微生物学检测。通过特异性引物结合聚合酶链式反应（Polymerase Chain Reaction，PCR）对分离菌株的毒力基因进行鉴定。本次研究共获得24株大肠杆菌分离株，其中75%的菌株携带肠毒素性感染典型的elt基因，检出率最高。未检测到分别常见于肠出血性大肠杆菌与肠致病性大肠杆菌的stx及bfpA基因。本次研究在圭亚那紫贻贝来源的大肠杆菌分离株中发现elt毒力相关基因，这提示亟需加强食品加工全流程的管理，包括落实良好操作规范、采用适宜的储存方式以及食用前充分烹煮，以保障消费者的健康安全。