Fate of Escherichia coli and Salmonella typhimurium in a Food Film on Stainless Steel at 5°C

Abstract

The fate of Escherichia coli and Salmonella typhimurium in a model system of food residue was determined. Bacteria were grown at 32°C in plate count broth or beef “serum”, placed on stainless steel, then dried at 5°C under quiescent or forced air and held for 24 h. Survival was determined by enumeration on plate count agar, and injury was determined by failure of E. coli to grow on violet red bile agar or S. typhimurium to grow on brilliant green agar. The physiological age of a culture was a major determinant of survival and injury. At the most vulnerable age of bacteria in plate count broth, approximately 99.9% of the cells died during the test period and 90% of the survivors was injured. In beef serum there was less death and injury than in plate count broth. The forced air environment was less destructive than the quiescent environment. The model system indicated bacteria in a food film may be in an unfavorable environment, and the surviving bacteria may not be enumerated with commonly used selective media.