SURVIVAL OF ESCHERICHIA COLI O157:H7 AND NON O157 STRAINS IN SYNTHETIC GASTRIC FLUID INOCULATED ON COMMERCIALLY AVAILABLE FRANKFURTERS

In this study acid resistance of STEC O157:H7 and non-0157 STEC serogroups of O26, O103 and O145 were investigated during storage of commercially available frankfurters. Pathogens were surface inoculated on frankfurters ca. 5 +/- 1 log cfu/g and the inoculated frankfurters were stored at 4 degrees C for 75 days. Microbiological analysis and pH measurements were conducted at days 0, 15, 30, 45, 60 and 75 of cold storage. In the first part of the study, different brands of commercially available frankfurters produced from cattle meat (Brand A, B, C, D, E) were investigated in order to evaluate which brand aided pathogen survival in acidic environment. Pathogen resistance to synthetic gastric fluid (SGF) was very weak in brands A, B, C, and D samples, and survivor counts were undetectable during SGF experiments after "Day 0" of the storage. These preliminary experiments showed that pathogens had stronger acid resistance on one brand of frankfurters, therefore in the second part of the study triplicate trials were conducted with this brand (Brand E). On brand E frankfurters, the pathogens were still detectable at the 45th day of storage after SGF exposure except for O157:H7. The gradual decrease in the pH of this brand of frankfurters might have aided acid resistance of the pathogens. Results show that in every brand of samples tested, the non-O157 serogroups had higher survivor counts than O157:H7, during storage and SGF experiments of frankfurters.