Isolation and characterization of thermal resistance of Salmonella strains from raw, frozen chicken nuggets, strips and pelleted broiler feeds

Raw, frozen chicken nuggets/strips have been identified as a significant risk factor in contracting food-borne salmonellosis. During processing, these products undergo partial frying to ensure their shape is maintained and give the batter and breaded coating a golden brown colour before they are frozen and packaged. This thermal treatment may mislead consumers to believe these products are fully-cooked, and that they require only re-heating before consumption. It is uncertain whether inadequate cooking (microwave oven) or the presence of Salmonella serovars with elevated thermal resistance is the more likely cause of salmonellosis associated with these products. Thermally resistant Salmonella strains may be selected by the heating step used in poultry feed pelleting and subsequently contaminate the animals, meat and enter the food distribution system.;Salmonellae were isolated using the Health Canada MFHPB-20 method for the isolation and identification of Salmonella from foods. Strains were characterized through serotyping, phage typing, antimicrobial resistance typing (R-type) and pulsed-field gel electrophoresis pattern analysis (pulse type).;Thermal resistances (D- and z-value) were determined for cocktails of the same Salmonella serovar. Cocktails were challenged in chicken nugget meat heat challenged in a preheated waterbath and recovered on tryptic soya broth containing 1.5% agar and 0.6% yeast extract with 48 h incubation at 25°C.;Salmonellae were isolated from 27% of chicken nuggets/strips, 5% of pelleted feed and from 48% of meat blend samples. Of the different serovars, S. Enteritidis was the only organism isolated from feed, nuggets/strips and meat blend. S. Enteritidis strains with identical phage- pulse- and R-types were isolated from feed and nugget meat blend samples, while nugget isolates had different phage and pulse type combinations.;This study was undertaken to determine the occurrence and characterize the strains of Salmonella contaminating raw, frozen chicken nuggets/strips and pelleted feeds in an attempt to demonstrate whether the same Salmonella strains present in broiler feed could be isolated from raw, frozen chicken nuggets/strips available for human consumption.;The thermal resistances found were lower than those reported for similar strains in the literature. D-values ranged from 6.93 to 0.12min at 55 and 62°C respectively, with z-values from 4.10 to 5.17°C. The two strains of S. Enteritidis separately isolated from pelleted feed and chicken nugget meat blend, with indistinguishable geno- and phenotypes, had lower (and probably identical) thermal resistances than the other isolates.;Results from this project indicate that indistinguishable Salmonella strains could be isolated from pelleted broiler feed and from meat blend used in the manufacture of raw, frozen chicken nuggets/strips. However results did not rule out the possibility that breeding stock or contamination during processing may have contributed to contamination by Salmonella . Thermal resistance data show that the strains did not exhibit unusually high thermal resistance, and that normal heating (71°C) prior to consumption should eliminate these organisms from chicken nuggets/strips. Future development of this research should focus on investigating the potential for post-pelleting contamination of pelleted feed in the pellet mill via contaminated dust and the extent to which antibiotic-resistant strains of Salmonella persist in raw chicken meat products.