Characterization and evaluation of Escherichia coli biotype I strains for use as surrogates for enteric pathogens in validation of beef carcass interventions

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Title: Characterization and evaluation of Escherichia coli biotype I strains for use as surrogates for enteric pathogens in validation of beef carcass interventions
Author: Cabrera-Diaz, Elisa
Abstract: 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 .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2513
Date: 2009-05-15

Citation

Characterization and evaluation of Escherichia coli biotype I strains for use as surrogates for enteric pathogens in validation of beef carcass interventions. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2513 .

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