Bactericidal effect of chlorine on Mycobacterium paratuberculosis in drinking water

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Abstract
Aims: One possible route of transmission of Mycobacterium paratuberculosis from cattle to humans is via contaminated water supplies. The aim of this work was to determine whether this organism can survive standard water treatment processes. Methods and Results: Two strains of M. paratuberculosis (bovine strain, NCTC 8578 and human strain Linda, ATCC 43015) were subjected to various chlorine concentrations (0·5, 1·0 and 2·0 μg ml–1) for 15 and 30 min. Chlorine test solutions were made up in two types of water, sterile water that had been deionized and subjected to reverse osmosis (DRO) and DRO water containing MgCl2, CaCl2, NaHCO3 and bovine serum albumin (0·3% w/v), the latter to mimic conditions the organism would experience in commercial water treatment operations. Conclusions: The data showed that when initial inoculum levels were high (106 cfu ml–1) neither M. paratuberculosis strain was completely killed at the free chlorine concentrations and contact times applied. Log10 reductions in the range 1·32–2·82 were observed. The greatest log10 reduction in cell numbers (2·82 and 2·35 for the bovine and human strains, respectively) was observed at the highest chlorine concentration (2 μg ml–1) and longest contact time (30 min). Significance and Impact of the Study: This work highlights the need for further research into the survival of M. paratuberculosis during water treatment.