Inactivation of Listeria Monocytogenes by Chlorine

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Abstract
Cells of Listeria monocytogenes strain Scott-A were harvested from cultures, washed, and then treated with a solution of sodium hypochlorite at 25°C and pH 7. The cells were more resistant to chlorine when they were (a) harvested from a 24-rather than 48-h-old culture, (b) grown in tryptose broth rather than on a slant of tryptose agar, and (c) washed and suspended using a 20 rather than 0.312 mM phosphate buffer solution. Cells of L. monocytogenes were exposed for 30 s-4 h to sodium hypochlorite solutions that contained 0.5–10 ppm available chlorine. Generally, the number of survivors decreased rapidly during the first 30 s followed by a slower decrease during the rest of the exposure time. The initial count of L. monocytogenes in the suspension (1 × 108–3.2 × 108/ml) decreased 0.49 to 6.4 orders of magnitude during the first 30 s of exposure to the chlorine solutions. The effect of the presence of organic substances on the strength of hypochlorite solutions was studied. Presence of 0.05 or 0.1% peptone ...