THE EFFECT OF LACTOCOCCUS LACTIS ON THE GROWTH CHARACTERISTICS OF LISTERIA MONOCYTOGENES IN ALFALFA SPROUT BROTH

Lactic acid bacteria isolated from commercially produced alfalfa sprouts were screened for activity against Listeria monocytogenes F4258. Most active isolates were identified as Lactococcus lactis subsp. lactis. The isolates fell into two categories, strains that inhibited by acid production only, and strains that appeared to have additional inhibitory activity. An acid-only isolate, SP26, was used to evaluate the effect of initial pH (5, 6, 7, 8) and temperature (10, 20, and 30 °C) on the interaction between the lactic acid bacterium and L. monocytogenes using “sprout juice” as a model system. The model system was inoculated with an initial level of approx. 103 CFU ml-1L. monocytogenes in both mono-culture controls and the co-cultures and the co-cultures with L. lactis (103-104 CFU ml-1). The primary inhibitory effect attributable to L. lactis was a 2 to 3 log cycle decrease in the maximum population density obtained by L. monocytogenes. The extent of the inhibition was decreased at 10 °C, but was only s...