Inhibition of Enteropathogenic Escherichia coli by Homofermentative Lactic Acid Bacteria in SkimmilkI. Comparison of Strains of Escherichia coli.

Behavior of enteropathogenic and nonpathogenic strains of Escherichia coli was determined when they were grown in skimmilk with and without 0.25 or 2.0% added lactic starter and incubated at 21 or 32 C for 15 h, and then after refrigeration at 7 C. With no lactics present, generation times for E. coli ranged from 28 to 35 min at 32 C and from 66 to 109 min at 21 C. At 32 C, after an initial 1- to 3-log increase in numbers and 6 to 9 h of incubation, E. coli was completely inhibited by both concentrations of starter culture. Complete inhibition of growth by E. coli occurred earlier at 32 than at 21 C, but smaller numbers of E. coli were obtained at 21 C; some strains virtually did not grow. The final pH of fermented milks ranged from 4.4 to 4.6. The longest survival time for E. coli in refrigerated fermented milk was about 17 days when milk was fermented at 32 C with 0.25% starter. A combination of lower incubation temperature (21 C) and higher starter concentration (2.0%) was most effective in controlling growth of E. coli in fermented skimmilk.