Competitive Growth of Listeria monocytogenes and Yersinia enterocolitica in Milk

Sterile whole milk and skim milk were inoculated with cultures of Yersinia enterocolitica (10 CFU/ml) and Listeria monocytogenes (15 CFU/ml) either separately or together and incubated at 4, 10, and 22°C. Unlike uninoculated control samples, growth of Y. enterocolitica with or without L. monocytogenes in whole milk or skim milk at 22°C and in whole milk at 10°C led to the development of off-odors with coagulation after heating to 80°C. Growth of Y. enterocolitica alone in whole milk and in skim milk at 4°C and in skim milk at 10°C did not result in any odor changes or coagulation. Similar or lower populations did not result in any character changes in trials with L. monocytogenes . In the presence of Y. enterocolitica , the growth of L. monocytogenes was found to be competitively inhibited in whole milk at temperatures of 10 and 22°C, but not at 4°C, whereas in skim milk no inhibition was observed at all the temperatures investigated.