Growth of E. coli in Cooked Ground Beef as Affected by Temperature

Introduction: Escherichia coli (E. coli) is a Gram negative bacteria that is commonly used as an indicator for fecal contamination. Several strains can be pathogenic and can cause serious foodborne illness. Since it is commonly found in ground beef, it is important to know its growth patterns at different temperatures in order to allow for safe food handling practices and avoid illness.

Purpose: To model the growth of E. coli in cooked ground beef at different temperatures over time.

Methods: Cooked ground beef was inoculated with E. coli ATCC 11229 and stored at four different temperatures (25, 35, 50, and 65°C) for 9 h. The beef was sampled every hour and plated on 3M™ Petrifilm™ E. coli/Coliform Count Plates, which were later enumerated for E. coli colonies.

Results: Two-log increases were seen at 25°C after 9 h, 35°C after 4.75 h, and 50°C after 3.5 h, but 65°C contained no detectable CFUs after 1 h. The most rapid growth was seen at 50°C, however other studies reported E. coli growth above 45°C to be irreproducible.

Significance: These results provide information on the growth of E. coli in cooked ground beef and can provide a basis for manufacturers in determining the microbial load of the product and safe holding time procedures. These findings also provide validation for USDA HACCP principles and guidelines.