Use of flourescent surrogate organisms for enteric pathogens in validation of carcass decontamination treatments
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During the harvesting process, meat products can become contaminated with enteric pathogens, such as Escherichia coli O157:H7 and Salmonella Typhimurium. Surrogates for these pathogens would be beneficial for validating carcass decontamination treatments. Surrogate organisms are organisms that behave similarly to specific pathogens but are non-pathogenic and can be used to determine efficacy of decontamination regimes for pathogens. The surrogates proposed are non-pathogenic, ampicillin-resistant E. coli biotype I strains that were previously isolated from beef cattle hides. Each E. coli strain was transformed to express a fluorescent protein (red: EcRFP; green: EcGFP; yellow: EcYFP) that is detectable under an ultraviolet light source. Surface areas on hot boned beef carcasses (clod, brisket, outside round) were inoculated with a fecal slurry containing EcRFP, EcGFP, EcYFP and rifampicin-resistant E. coli O157:H7 and S. Typhimurium. Surface regions were then treated in a model spray cabinet using an initial water wash (28ºC) followed by treatments using 2% L-lactic acid (55ºC), hot water (95ºC at source) or a combination of the two. Treatments were compared for their effectiveness at reducing populations of inoculated (4.7 to 6.7 log CFU/cm2) E. coli, S. Typhimurium, EcRFP, EcGFP and EcYFP. Log reductions for inoculated organisms were calculated individually and then total and average surrogate cocktail values were calculated. All decontamination treatments reduced the inoculated numbers of pathogens and surrogates to near or below the detection limit of 0.5 log CFU/cm2. The combined treatment resulted in the greatest log reductions. The three individual surrogate organisms varied in log reductions according to the different decontamination treatments applied; however, log reductions for the total surrogate cocktail did not differ significantly from that of E. coli O157:H7. With the exception of EcYFP, the individual surrogates and average surrogate cocktail were significantly more resistant to microbial interventions including lactic acid than S. Typhimurium. Because abattoirs utilize different carcass decontamination treatments, it is difficult for one single fluorescent protein-producing isolate to accurately represent the behavior of E. coli O157:H7 or S. Typhimurium. Instead, surrogates should be used as a total cocktail to accurately represent the effectiveness of different treatments for reduction of enteric pathogens.
Moseley, Tiffany Marie (2007). Use of flourescent surrogate organisms for enteric pathogens in validation of carcass decontamination treatments. Master's thesis, Texas A&M University. Available electronically from