Narrow Results

The extended distribution of L. monocytogenes in the environment and its ability to persist in food-processing environments cause the frequent contamination of foods, which represents the main source of human infection. Our objective was to assess the effect of chlorine water treatment on L. monocytogenes and to study this organism's survival strategies in chlorinated water.

RNA content, 16S rRNA (FISH), DNA content (16S rDNA and hlyA gene), culturability and substrate responsiveness combined with FISH detection (DVC-FISH assay) were assessed. L. monocytogenes cell culturability was lost after 2h in drinking water with 0.16 and 1 mg/L of free chlorine. Viability was conserved for more than 16 hours at minor chlorine concentrations. Both, the 16S rDNA gene amplicon and the hlyA fragment, specifics for L. monocytogenes, were detected after a 24-hour chlorine exposure. 16S RNA levels were constant during chlorine treatment, thus chlorine-damage of bacteria is unlikely to involve ribosome degradation. Combinied modified DVC and FISH techniques can rapidly and specifically detect and identify viable L. monocytogenes cells in water samples. Some normal disinfection practices used in drinking water treatment (free chlorine lower than 0.2 mg/L) proved to be inadequate at short time of exposition to control this organism, as it could survive in VBNC state, what can become a public health risk.