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 从食品中分离大肠埃希菌（Escherichia coli）是一项重要的公共卫生关切事项。该菌的致病菌株可引发从腹泻到溶血性尿毒综合征的多种疾病。为此，本研究针对巴西巴伊亚州卡舒埃拉市市售圭亚那贻贝（Mytella guyanensis）中分离得到的大肠埃希菌菌株的毒力基因展开了调查。

实验样本从4个销售摊位采购：2个来自超市，2个来自集市摊位。样本置于配备可重复使用冰袋的保温箱中运送至实验室开展分析。经微生物学检测后，在伊红美蓝琼脂（eosin methylene blue agar）平板上分离得到大肠埃希菌菌株，将其保存在添加15%甘油的脑心浸液培养基（brain-heart infusion medium）中，并于-20 ℃条件下储存。通过特异性引物结合聚合酶链反应（Polymerase Chain Reaction，简称PCR）鉴定分离菌株的毒力基因。

本研究共获得24株大肠埃希菌分离株，其中75%的分离株携带肠毒素性感染相关的elt基因，该基因的检出率最高。未检出分别常见于肠出血性大肠埃希菌和肠致病性大肠埃希菌的stx基因与bfpA基因。从圭亚那贻贝分离的大肠埃希菌中检出elt毒力相关基因，这一结果提示亟需加强食品加工、储存及流通环节的管理，落实良好操作规范，采用适宜的储存方式并确保食用前充分烹煮，以切实保障消费者健康。