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-degrees-C. Unlike uninoculated control samples, growth of Y. enterocolitica with or without L monocytogenes in whole milk or skim milk at 22-degrees-C and in whole milk at 10-degrees-C led to the development of off-odors with coagulation after heating to 80-degrees-C. Growth of Y enterocolitica alone in whole milk and in skim milk at 4-degrees-C and in skim milk at 10-degrees-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-degrees-C, but not at 4-degrees-C, whereas in skim milk no inhibition was observed at all the temperatures investigated.