Investigating the survival and acid resistance of shigatoxin producing Escherichia coli in frankfurters

In this study, survival and synthetic gastric fluid resistance of E.coli O157:H7 and "big six" non-O157 serogroups; O103, O26 and O145 were investigated during storage at 4°C of frankfurters. Frankfurters obtained from local stores and experimentally produced frankfurters were inoculated with the STEC pathogens (around 5,0+1,00 log10cfu/g) and stored in vacuum packages for 75 days. Pathogen counts and acid survival in synthetic gastric fluid were evaluated on 0, 15, 30, 45, 60 and 75 days of storage.Treatment groups were divided as frankfurters obtained from stores (Group 1A and Group 1B) and experimentally produced frankfurters (Group 2). The pathogens did not show any resistance to synthetic gastric fluid after the first day (Day 0) of storage in Group 1A samples. The results of experiments on Group 1A samples showed, on one brand of frankfurters pathogens had longer synthetic gastric fluid resistance and therefore this brand was chosen for further experiments. Frankfurters of this brand were grouped as Group 1B and triplicate experiment results were reported. Synthetic gastric fluid experiments in this group of samples showed that pathogen counts during SGF exposure decreased below detection limit after 60 days of storage for STEC O26 and O145, on the 75th day for STEC O103 and after 45 days for STEC O157. After obtaining the results from the Group 1A and Group 1B frankfurters, experimental production was performed and these samples were grouped as Group 2. In this group of samples STEC O157 survival during synthetic gastric fluid exposure decreased after 45 days of storage and decreased below detection limit on the 75th day of storage. On the other hand STEC O103, O26 and O145 survived the SGF exposure for 90 minutes even on the 75th day of storage. As a result of this study, it can be concluded that survival and synthetic gastric fluid resistance of STEC pathogens were affected by factors such as strain, pH of the frankfurter, and competitive microflora. Taking into account that the STEC infective dose is quite low, it can be said that frankfurters might pose a food safety risk if STEC contamination occurs.