Isolation and characterization of non-O157 Shiga toxin-producing Escherichia coli from beef carcasses, cuts and trimmings of abattoirs in Argentina

Several foods contaminated with Shiga toxin-producing Escherichia coli (STEC) are associated with human diseases. Some countries have established microbiological criteria for non-O157 STEC, thus, the absence of serogroups O26, O45, O103, O104, O111, O121, and O145 in sprouts from the European Union or ground beef and beef trimmings from the United States is mandatory. While in Argentina screening for O26, O103, O111, O145 and O121 in ground beef, ready-to-eat food, sausages and vegetables is mandatory, other countries have zero-tolerance for all STEC in chilled beef. The aim of this study was to provide data on the prevalence of non-O157 STEC isolated from beef processed in eight Argentinean cattle slaughterhouses producing beef for export and local markets, and to know the non-O157 STEC profiles through strain characterization and genotypic analysis. Samples (n = 15,965) from 3,205 beef carcasses, 9,570 cuts and 3,190 trimmings collected between March and September 2014 were processed in pools of five samples each. Pools of samples (n = 3,193) from 641 carcasses, 1,914 cuts and 638 trimming were analyzed for non-O157 STEC isolation according to ISO/CEN 13136:2012. Of these, 37 pools of carcasses (5.8%), 111 pools of cuts (5.8%) and 45 pools of trimmings (7.0%) were positive for non-O157 STEC. STEC strains (n = 200) were isolated from 193 pools of samples. The most prevalent serotypes were O174:H21, O185:H7, O8:H19, O178:H19 and O130:H11, and the most prevalent genotypes were stx2c(vh-b) and stx2a/saa/ehxA. O103:H21 strain was eae-positive and one O178:H19 strain was aggR/aaiC-positive. The prevalence of non-O157 STEC in beef carcasses reported here was low. None of the non-O157 STEC strains isolated corresponded to the non-O157 STEC serotypes and virulence profiles isolated from human cases in Argentina in the same study period. The application of microbiological criteria for each foodstuff should be determined by risk analysis in order to have a stringent monitoring system. Likewise, zero-tolerance intervention measures should be applied in beef, together with GMP and HACCP. Further, collaborative efforts for risk assessment, management and communication are extremely important to improve the safety of foodstuffs.

多种受产志贺毒素大肠杆菌（Shiga toxin-producing Escherichia coli, STEC）污染的食品与人类疾病密切相关。目前已有部分国家针对非O157型STEC制定了微生物学标准：欧盟要求芽苗菜不得检出O26、O45、O103、O104、O111、O121及O145血清群，美国则强制要求绞碎牛肉与牛肉碎料中不得检出上述血清群。阿根廷则规定需在绞碎牛肉、即食食品、香肠及蔬菜中筛查O26、O103、O111、O145及O121血清群；另有部分国家对冷却牛肉中的所有STEC实施零容忍政策。本研究旨在为阿根廷8家肉牛屠宰场（其牛肉产品面向出口及本地市场）加工的牛肉中分离得到的非O157型STEC流行率提供数据支撑，并通过菌株表征与基因型分析明确非O157型STEC的分子特征。研究于2014年3月至9月间采集样本共计15965份，包括3205份牛胴体样本、9570份牛肉切块样本及3190份牛肉碎料样本，每份检测池由5份样本混合制备。其中，针对来自641份牛胴体、1914份牛肉切块及638份牛肉碎料的3193个混合样本，按照ISO/CEN 13136:2012标准开展非O157型STEC分离检测。结果显示，37个牛胴体混合样本（占比5.8%）、111个牛肉切块混合样本（占比5.8%）及45个牛肉碎料混合样本（占比7.0%）呈非O157型STEC阳性。最终从193个混合样本中分离得到200株STEC菌株。最常见的血清型为O174:H21、O185:H7、O8:H19、O178:H19及O130:H11；优势基因型为stx2c(vh-b)与stx2a/saa/ehxA。其中1株O103:H21菌株呈eae阳性，1株O178:H19菌株呈aggR/aaiC阳性。本研究报道的牛胴体非O157型STEC流行率较低，且所有分离得到的非O157型STEC菌株，其血清型与毒力特征均与同期阿根廷人类病例中分离得到的菌株不相符。食品的微生物学标准制定应基于风险分析，以构建严格的食品安全监控体系。同时，需结合良好生产规范（Good Manufacturing Practice, GMP）与危害分析与关键控制点（Hazard Analysis and Critical Control Points, HACCP）体系，对牛肉实施零容忍干预措施。此外，加强风险评估、风险管理与风险沟通的跨领域协作，对提升食品整体安全性至关重要。