METABOLIC ACTIVITY OF LUX-MARKED ESCHERICHIA COLI O157:H7 DURING PRODUCTION AND STORAGE OF YOGURT

Abstract

The objective of this study is to estimate the metabolic activity and survival ofbioluminescence Escherichia coli O157:H7 (a chromosomally lux-marked strain) duringproduction and storage of yogurt.The effect of temperature on activity and survival of E.coli O157:H7 during the production of yogurt were studied by incubating inoculated milkat 43°C, 40 °C and 37 °C. The results showed that E. coli O157:H7 activity and cellcounts increased immediately in all yogurt samples at the beginning stagesoffermentation then they declined to nearly of the initial levels at the end of fermentation.During storage yogurt at three different initial levels of pH (4.6, 4.3 and 4.0), significantdifferences (p<0.001) were found in cell activity and viable cellcount of Escherichia coliO157:H7, indicating that low pH provided ideal conditions to inhibit the activity ofpathogens. The cell activity and survival of E. coli O157:H7 were significantly differentduring storage at three different temperatures (4 °C, 12 °C and 25 °C). At 25 °C, E. coliO157:H7 activity and cell counts were significantly lower (P<0.001) compared withother storage temperatures. Bioluminescence (metabolic activity) helps to track E.coliO157:H7 growth and survival during manufacture and storage of yogurt and interact withtheir acidic environments as a rapid assay method. Therefore, it can provide notice on theway of eliminating E.coli O157:H7 in the dairy products to avoid these pathogens