Reduction of pathogenic bacteria in ground beef using a Lactobacillus based biological intervention



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Two pathogenic bacteria that can be found in ground beef are Escherichia coli (E.coli) O157:H7 and Salmonella. Six additional non-O157 Shiga toxin-producing E.coli (STEC) serogroups were declared adulterants in raw ground beef by the USDA-FSIS, posing additional concerns to the industry. The objective of this project was to evaluate the efficacy of biological intervention with lactobacillus multi-species strains - Lactobacillus acidophilus (NP51 and NP28), Pediococcus acidilactici (NP3) and Lactococcus lactis subsp. lactis (NP7) on the reduction of E. coli O157:H7, Salmonella and non-O157 STEC populations in ground beef during retail display. Coarse ground beef (22.68 kg) was inoculated with cocktail mixtures of either E. coli O157:H7 or Salmonella or non-O157 STECs and mixed to assure uniform pathogen distribution. Coarse ground beef was then divided into two equal portions - Control (CON) and Lactobacillus based biological intervention-treated (LAC). The LAC treatment was prepared by adding potable water to each of the aforementioned freeze-dried strains (NP51 and NP28 at 109 CFU/mL and NP3 and NP7 at 108 CFU/mL) and mixed to make the cocktail to achieve final desired concentration of 107 CFU/g pn the meat. After preparation, 50 mL of the LAC treatment was added to the inoculated ground beef and thoroughly mixed before grinding. Similarly, CON ground beef was finely ground without the application of LAC treatment. Finely ground meat from both treatments was portioned on black expanded polystyrene trays before overwrapping with polyvinyl chloride film. Packages were arranged in a retail display case (0 to 4°C) and samples were collected on d - 1, 3, and 5. At each sampling interval, ground beef samples were stomached in buffered peptone water (BPW) before serial dilution. All the dilutions are plated in duplicates onto MacConkey, Xylose Lysine Deoxycholate (XLD) and deMan Rogosa Sharpe (MRS) agar plates for enumeration of for E. coli, Salmonella and Lactobacillus samples, respectively. On day 1, there were no reduction in microbial count due to LAC treatment with the LAC counts being the same as the CON. Total pathogens in the CON samples changed over time. The total E. coli O157:H7 counts in CON samples are not significantly (P>0.05) from day 1 to day 5 of the display, while significant (P<0.05) decrease was observed in the number of E. coli O157:H7 in LAC samples on day 3 and day 5 when compared to day1. Furthermore, LAC samples had significantly (P < 0.05) less E. coli O157:H7 on days 3 and 5 of retail display than CON. This suggests that LAC was a slight inhibitory toward E. coli O157:H7 proliferation in the treated samples with populations being 0.35 and 1.02 log CFU/g lower than the CON samples on days 3 and 5, respectively. A similar trend was observed in ground beef inoculated with Salmonella. The populations of LAC samples are 0.9 and 1.44 log CFU/g lower than the CON on days 3 and 5 respectively. Regarding non-O157 STECs, LAC samples had significantly fewer (P < 0.05) pathogen populations on day 5 when compared to CON ground beef. STEC populations were 1.5 log cycles less in LAC samples when compared to CON samples on day 5. These results suggest the addition of NP51 + NP28 + NP7 + NP3 strains of Lactobacillus to ground beef may not be an effective intervention to elimante the levels of E. coli O157:H7, Salmonella and non-O157 STECs but helped to inhibit the proliferation of the aforementioned bacteria in overwrap packaging during extended retail display



Lactic acid bacteria, Ground beef, E. coli O157:H7, Salmonella, Non-O157 STECs, Overwrap packaging