부산대학교 도서관

Growth curves were generated for Escherichia coliO157:H7 in brain–heart infusion broth incubated at 37 or 15°C in the presence of individual and combinations of competing microflora. Broths were inoculated withE. coliO157:H7 (log103·00 cfu ml−1) and competitors (log104·00 cfu ml−1) and the initial pH of the broth was either neutral (7·0) or adjusted to 5·8 and then sequentially reduced to 4·8 over 10 h to simulate fermentation conditions. Growth curves were also generated for the competitors in these cultures, including Pseudomonas fragi, Hafnia alvei, Pediococcus acidilactici(pepperoni starter culture) and Brochothrix thermosphacta. Gompertz equations were fitted to the data and growth kinetics including lag phase duration, exponential growth rates and maximum population densities (MPD) calculated. In pure culture, the growth parameters for E. coliO157:H7 in neutral pH broths were significantly different from those recorded in simulated fermentation broths (P<0·05). The presence of competitors in the broth also had a significant effect on the growth kinetics of the pathogen. H. alveisignificantly inhibited the growth (lag phase, growth rate and MPD) of E. coliO157:H7 at 37°C, neutral pH and outgrew the pathogen under these conditions. In neutral pH cultures, two other competitors, B. thermosphactaand P. acidilacticialso inhibited the lag phase of the pathogen but had no effect on the other growth parameters. In simulated fermentation broths, the growth rate of E. coliO157:H7 was consistently slower and the MPD lower in the presence of a competitive microflora than when grown individually. At 15°C, only one competitor, P. fragisignificantly inhibited the lag phase of the pathogen. The implications of these findings for food safety are discussed.