Inhibition Activity of Lactic Acid Bacteria against Salmonella, Escherichia coli O157:H7 and non-O157 STECs in Ground Beef

Introduction: Salmonella, Escherichia coli O157:H7 and non-O157 STEC are pathogens capable of causing high morbidity and mortality among humans, with the majority of infections linked to the consumption of contaminated meat and meat products. Although many intervention methods are commonly applied to beef carcasses, very few interventions have been validated to be effective in ground beef.

Purpose: The objective of this study was to evaluate the effect of different cocktails of lactic acid bacteria (LAB) on the growth and survival of Salmonella, Escherichia coli O157:H7 and non-O157 STECs in ground beef during refrigerated storage.

Methods: Four LAB cocktails including NP51+C28, NP51+C28+D3, NP51+C28+L7+D3 and NP51+D3+L7+M35 were added at 1 x 10⁷ CFU/g of ground beef containing a pathogen concentration of 10³ CFU/g. Samples were stored at 4 °C , and pathogen enumeration was evaluated on days 0, 1, 3 and 5.

Results: Compared with control sample, there were significant (P < 0.05) reductions on all of the pathogens in the ground beef samples treated with all LAB cocktails during 5 days of refrigerated storage. LAB cocktails of NP51+D3+L7+M35 and NP51+C28+D3 displayed significantly stronger (P < 0.05) inhibition activities than the other two (NP51+C28 and NP51+D3+L7+M35). On day 5, the most significant reductions on Salmonella (1.42 log CFU/g), Escherichia coli O157:H7 (1.45 log CFU/g) and non-O157 STEC (1.08 log CFU/g) were observed after the application of NP51+D3+L7+M35.

Significance: The treatment of LAB cocktails is a very effective intervention for ground beef to control Salmonella, Escherichia coli O157:H7 and non-O157 STECs. LAB cocktails can be provided to processors in various forms (frozen, liquid or freeze-dried) and application can be easily implemented into current operations by adding the cocktails into ground beef products during processing.