Bactericidal effect of chlorine on Mycobacterium paratuberculosis in drinking water

Aims: One possible route of transmission of Mycobacterium paratuberculosis from cattle to humans is via contaminated water supplies. The aim of this w ork was to determine whether this organism can survive standard water treat ment processes. Methods and Results: Two strains of M. paratuberculosis (bovine strain, NCT C 8578 and human strain Linda, ATCC 43015) were subjected to various chlori ne concentrations (0.5, 1.0 and 2.0 mug 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 contain ing MgCl2, CaCl2, NaHCO3 and bovine serum albumin (0.3% w/v), the latter to mimic conditions the organism would experience in commercial water treatme nt operations. Conclusions: The data showed that when initial inoculum levels were high (1 0(6) Cfu ml(-1)) neither M. paratuberculosis strain was completely killed a t the free chlorine concentrations and contact times applied. Log(10) reduc tions in the range 1.32-2.82 were observed. The greatest log(10) reduction in cell numbers (2.82 and 2.35 for the bovine and human strains, respective ly) was observed at the highest chlorine concentration (2 mug ml(-1)) and l ongest contact time (30 min). Significance and Impact of the Study: This work highlights the need for fur ther research into the survival of M. Paratuberculosis during water treatme nt.