EFFECT OF GROWTH TEMPERATURE AND MEDIA ON INACTIVATION OF LISTERIA-MONOCYTOGENES BY CHLORINE

The objective of this study was to determine the effect of growth environment on the susceptibility of Listeria monocytogenes to inactivation by hypochlorite sanitizer. Cells were grown in tryptic soy broth (TSB) at 35, 21, and 6-degrees-C and in 1:15 dilution of TSB (low nutrient medium, LNM) at 35-degrees-C. Late exponential phase cells were harvested, washed, and exposed to a 1 ppm sodium hypochlorite solution for periods up to 5 min. After 30 s exposure, cells grown at 35-degrees-C in TSB were reduced in number by 2.1 +/- .3, at 21-degrees-C, 3.1 +/- .3 and at 6-degrees-C, 3.4 +/- .3 log units. After 30 s exposure to 5 ppm free chlorine cells grown at 35-degrees-C in TSB were reduced in number by 5.2 +/- .2 and in LNM by 3.1 +/- .1 log units. These data demonstrate that growth environment has a significant effect on chlorine inactivation of L. monocytogenes.