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，以下简称E. coli）是学界高度关注的重要课题。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商业化售卖的圭亚那偏顶蛤（Mytella guyanensis）中分离得到的大肠杆菌菌株的毒力基因展开了调查。实验样本购自4个售卖点位：2家超市与2个农贸市场摊位。样本采用配备可重复使用冰袋的恒温箱封装，运送至实验室开展检测分析。经微生物学检测后，通过伊红美蓝琼脂（eosin methylene blue agar）分离得到大肠杆菌菌株，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。采用特异性引物结合聚合酶链式反应（Polymerase Chain Reaction，PCR）鉴定分离菌株的毒力基因。本次实验共获得24株大肠杆菌分离株，其中75%的菌株携带肠毒素性大肠杆菌标志性的elt基因。未检测到分别常见于肠出血性大肠杆菌和肠致病性大肠杆菌的stx基因与bfpA基因。圭亚那偏顶蛤源大肠杆菌分离株中elt毒力相关基因的检出结果表明，亟需优化食品加工全流程，落实规范操作、合理储存及食用前充分烹煮等措施，以保障消费者健康。