Fate of pathogenic and non-pathogenic Escherichia coli strains in two fermented milk products

The growth and survival of pathogenic and non-pathogenic strains of Escherichia coli was determined in traditionally fermented pasteurized and unpasteurized milk and in Lacto, an industrially fermented milk. Each milk treatment was incubated at 20 degrees C for 24 h and then stored at either 20 degrees C or 5 degrees C for 96 h. Lacto inhibited all the three E. coli strains. Two strains could not be recovered and the third survived only in very low numbers after 24 h storage of Lacto at both 20 degrees C and 5 degrees C. All three E. coli strains survived and multiplied to maximum cell numbers in the range 10(7)-10(9)/ml during traditional fermentation of unpasteurized milk. Cell numbers decreased to 10(3)-10(6) and 10(2)-10(5) during storage of the fermented product at 20 degrees C and 5 degrees C respectively. Higher maximum numbers, 10(9)-10(10), of the three strains of E. coli were attained during traditional fermentation of pasteurized milk. The numbers decreased to 10(5)-10(8) and 10(4)-10(7) during storage of the fermented product at 20 degrees C and 5 degrees C respectively. Generally, fewer E. coli survived when the fermented milk products were stored at refrigeration temperature.