Evaluation of Potential for Inhibition of Growth of Escherichia coli O157:H7 and Multidrug-Resistant Salmonella Serovars in Raw Beef by Addition of a Presumptive Lactobacillus sakei Ground Beef Isolate

Abstract

The efficacy of adding presumptive Lactobacillus sakei (LS) strain 10-EGR-a, the most inhibitory from among 12 ground beef Lactobacillus isolates, to inhibit growth by Escherichia coli O157:H7 and multidrug-resistant (MDR) Salmonella (serovars Newport and Typhimurium) was evaluated in a beef-derived broth medium at 10°C and in fresh raw ground beef at 10 and 5°C. Pathogen inhibition was observed in the broth medium at both high (108:105 to 107:105) and low (106:105 to 105:105) LS:pathogen ratios. After 9 days at 10°C, in broth medium with high LS:pathogen ratios, growth of E. coli O157:H7 and MDR Salmonella was inhibited by an average of 2.6 and 3.2 log CFU/ml, respectively, whereas in broth medium with low LS:pathogen ratios, E. coli O157:H7 and MDR Salmonella growth was inhibited by an average of 2.8 and 1.8 log CFU/ml, respectively. However, in raw ground beef no significant inhibition was seen with LS:pathogen ratios of 105:102 to 105:103. Significant inhibition was seen at very high LS:pathogen ratios (106 to 107:102 to 103), but gross spoilage of the product occurred by day 6. Although presumptive LS 10-EGR-a can inhibit growth of E. coli O157:H7 and MDR Salmonella in a beef-derived broth medium, the inability to produce similar results in ground beef without deleteriously affecting the quality of the product is a limitation that needs further investigation.