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Description:
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Antimicrobial interventions implemented in slaughter establishments for the
reduction of enteric pathogens on beef carcasses must be validated to demonstrate
efficacy under commercial operation conditions . Validation studies can be conducted
using surrogates which are nonpathogenic organisms that respond to a particular
treatment in a manner equivalent to a target pathogen . The purpose of this study was to
identify surrogates for enteric pathogens to validate antimicrobial interventions on beef
carcasses . The growth , attachment , resistance properties as well as the response to
interventions on beef carcasses of nonpathogenic fluorescent protein -marked E . coli
strains were evaluated and compared to E . coli O157 :H7 and Salmonella strains .
Growth curves were performed in tryptic soy broth at 37°C and it was
demonstrated that in general , growth parameters were not different among surrogates
and target pathogens . Thermal resistance was compared in phosphate buffered saline
(PBS ) at 55 , 60 and 65°C ; D -values of surrogates were not different or were higher than those of target pathogens . The acid resistance of surrogates was not different to that of E .
coli O157 :H7 in PBS acidified with lactic acid at pH 2 .5 , 3 .0 and 3 .5 . Some Salmonella
serotypes were found to be less acid resistant than the surrogates . Survival of surrogates
after storage at low temperatures (4°C and -18°C ) was not different or was longer than
survival of E . coli O157 :H7 and Salmonella . Additionally , the cell surface
hydrophobicity and attachment to beef carcasses surfaces was not different among
surrogates and pathogens . Antimicrobial interventions were applied on carcass surfaces
under laboratory controlled conditions . After application of hot water washes , D -values
were not different among surrogates and pathogens , while no differences were observed
in log reductions (CFU /cm2 ) among surrogates and pathogens when 2 % L -lactic acid
sprays at 25 and 55°C were applied , regardless of the temperature and volume of the
acid solution . The response of surrogates to water washes and lactic acid sprays on beef
carcasses was also evaluated in commercial slaughter facilities . Reductions of surrogates
were not different to those of aerobic plate count , coliforms and E . coli . However , the
surrogates showed less variation and provided more consistent results than traditional
indicators . |