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

F eresu , S. & N yati , H. 1990. Fate of pathogenic and non‐pathogenic Escherichia coli strains in two fermented milk products. Journal of Applied Bacteriology 69 , 814–821. 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 20d̀C for 24 h and then stored at either 20d̀C or 5d̀C 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 20d̀C and 5d̀C. 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 20d̀C and 5d̀C 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 20d̀C and 5d̀C respectively. Generally, fewer E. coli survived when the fermented milk products were stored at refrigeration temperature.