Penicillium camemberti and Penicillium roqueforti Enhance the Growth and Survival of Shiga Toxin-Producing Escherichia coli O157 under Mild Acidic Conditions

摘要

The effects of secondary starter molds of common mold-ripened cheeses on the Shiga toxin-producing Escherichia coli (STEC) O157 were assessed in 3 model systems. In the 1st model, 8 STEC Ol57 strains were incubated in the spent culture of Penicillium camemberti or Penicillium roqueforti under mild acidic conditions at 25 ℃. In the spent cultures of the mold at pH 4.8 to 5.0, the lag times of STEC O157 growth were significantly shorter than those observed in fresh medium. Analyses of the spent culture of P. camemberti showed that the causative agents of'the growth enhancement were produced by the mold in response to an acidic environment and were not fully inactivated! in heat treatment. In the 2nd model, P. camemberti and STEC O157 were cocultured in acidified milk at 25 ℃. The population of STEC O157 reached 108 CFU/mL in the presence of the mold, whereas the population steadily declined in the absence of the mold. Although this growth enhancement was partially attributable to alkalization by the mold, it was observed even when the pH of this model was stabilized. In the 3rd model, 2 STEC O157 strains were incubated in the ipent cultures of molds at pH 4.5 at 10 ℃. In the spent culture, proportions of injured cells were significantly lower and D values were significantly higher than those in control, except one STEC O157 strain in the spent culture of/? camemberti. These results showed that the molds could enhance the growth and survival of STEC O157 by changing the environment.