Cabrera-Diaz, Elisa (2007-12). Characterization and evaluation of Escherichia coli biotype I strains for use as surrogates for enteric pathogens in validation of beef carcass interventions. Doctoral Dissertation. Thesis uri icon

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.
  • 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.

publication date

  • December 2007