SURVIVAL OF LISTERIA MONOCYTOGENES AT DIFFERENT TEMPERATURES IN BROTH SUPPLEMENTED WITH SODIUM CHLORIDE

Growth and survival of Listeria monocytogenes (strains Scott A and V7) with sodium chloride levels ranging from 0 to 10% were studied in Tryptose Broth (TB) at 13, 4 and -18°C. As the incubation temperature is increased, the organisms are able to grow in the presence of higher levels of sodium chloride. At 13°C the two serotypes were able to increase in numbers in up to 9 to 10% NaCl. At 4°C counts decreased with increasing NaCl concentrations over the 12-day period, but the organism survived in substantial numbers. At -18°C there was a large initial decline in counts with little subsequent change. Low levels of salt were found to stimulate growth of Listeria monocytogenes which was more pronounced at 13°C. A three way analysis of variance using the mean log CFU/ml broth showed holding time, Listeria strains, NaCl concentrations and their interaction to be significantly important for survival of the bacteria at different holding temperatures.