Survival and viability of Helicobacter pylori after inoculation into chlorinated drinking water

The aim of this work was to assess the effect of chlorine water treatment on Helicobacter pylori and to study the succession of cellular alterations in response to chlorine exposure. H. pylori NCTC 11637 reference strain was used for inoculating water samples. The culturability, substrate responsiveness combined with fluorescent in situ hybridization detection (DVC-FISH assay), RNA content, DNA content, and mRNA changes of H. pylori cells were analyzed. Culturability was lost at 5 min in water with 0.96 mg/l of free chlorine. Viable cells were detected by DVC-FISH after 3 h of exposure to chlorine but not after 24 h. The percentage of coccoid forms was higher than spiral forms after 40 s of chlorine exposure, but even after 24 h, FISH detection revealed the presence of spiral cells. After 24 h, amplification of the specific H. pylori 16S rDNA gene was achieved. Expression of the vacA gene was detected with the same intensity at all time points tested, demonstrating that these genes are expressed in non-culturable H. pylori cells. Levels of 16S rRNA were constant during the chlorine treatment, so killing of bacteria with chlorine probably does not involve ribosome degradation. According to our results, H. pylori could survive to disinfection practices normally used in drinking water treatment in the viable but nonculturable form, which would allow them to reach final consumption points and, at the same time, enable them to be undetectable by culture methods. (C) 2007 Elsevier Ltd. All rights reserved.