Prevalence and numbers of Escherichia coli O157:H7 in minced beef and beef burgers from butcher shops and supermarkets in the Republic of Ireland

Abstract

This study investigated the prevalence and numbers of Escherichia coli O157:H7 in minced beef and beef burgers in supermarkets and butcher shops in the Republic of Ireland. Fifteen samples were collected quarterly from each of 26 counties over a 13-month period. All samples ( n=1533) were (1) directly plated on SMAC, and (2) enriched in mTSB with novobiocin, extracted by immunomagnetic separation (IMS), plating onto SMAC-CT agar and finally confirmed by PCR. Overall, E. coli O157:H7 was recovered from 43 samples (2.80%) with counts ranging from <0.52–4.03 log 10 cfu g −1. Of the positive samples, 2.70% (32/1183) were purchased from supermarkets and 3.14% (11/350) from butcher shops. Only one product type (fresh unpacked burgers from supermarkets) was negative for E. coli O157:H7. Of the products containing the pathogen, fresh packaged burgers from supermarkets had the highest prevalence of 4.46% (7/157) while fresh unpackaged mince purchased from supermarkets had the lowest prevalence of 2.01% (6/299). Of the 43 isolates recovered, 41 possessed verotoxin-producing genes ( vt1 and vt2), E. coli attaching and effacing gene ( eaeA), haemolysin gene ( hlyA), 60-MDa plasmid or rfb gene cluster that encodes for the biosynthesis of the O-antigen (pO157) and flagellar H7 antigen encoding gene ( fliC h7). The remaining 2/43 isolates contained only one of the verotoxin-producing genes ( vt1 or vt2) and all the other genes named.