Survival of Escherichia coli o157: h7 co-cultured with different levels of Pseudomonas fluorescens and Lactobacillus plantarum on fresh beef

ABSTRACT

The purpose of this study was to investigate the effect of different levels of Pseudomonas fluorescens (10² and 10(6)log10 cfu/ml)and Lactobacillus plantarum (10² and 10(4)log10 cfu/ml)on the growth of Escherichia coli O157H7 on beef loins. Beef loins inoculated with E. coli O157H7 and P. fluorescens were aerobically stored for 7 days at 4 ºC, while those inoculated with E. coli O157H7 and L. plantarum were vacuum packaged and stored for 8 weeks at 4 ºC. Aerobic Plate Counts (APC), E. coli O157H7 and either P. fluorescens or L. plantarum counts were determined at different storage intervals. For the aerobically packaged beef loins, E. coli O157H7 was detected throughout the 7 day storage period regardless of the P. fluorescens level in the inoculum. For the vacuum packaged beef loins, similar inoculum levels of E. coli O157H7 and L. plantarum allowed E. coli O157H7 to survive until week 5 of storage, while a higher inoculum level of L. plantarum inhibited E. coli O157H7 from week 3. Once fresh beef has been contaminated with E. coli O157H7, the level of P. fluorescens in the background flora does not inhibit its survival and growth. However, under vacuum storage, the application of L. plantarum as a biopreservative inhibits the survival of E. coli O157H7 on beef. The higher the level of L. plantarum in the system, the earlier the onset of the inhibition. Farmers and abattoirs have to strengthen preventive strategies to eliminate contamination of beef carcasses with E. coli O157H7.