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Mycobacterium avium is a waterborne opportunistic pathogen commonly detected indrinking water. The resistance of M. avium to common chemical disinfectants at a widerange of temperatures and pH levels allows this microorganism to persist in drinkingwater distribution systems. The mechanisms responsible for the survival of M. aviumin drinking water are not well understood. The persistence of M. avium in distributionsystems has been associated to their presence in biofilms or suspended particles insidewhich these microorganisms appear to gain protection against disinfectant attack.Because chlorine reacts with biofilm or particulate organic matter, the embedded cellsare exposed to lower disinfectant concentrations. Previous work (Tong et al., 2002)has shown that a relatively low concentration of monochloramine ( 1 mg/L as Cl2) at20oC and pH 8 could trigger an adaptive response, which made the bacteria about 2.8times more resistant than the ones treated with a relatively high concentration ofmonochloramine ( 5 mg/L as Cl2). Furthermore, preliminary results in this studysuggested that once the adaptive response was triggered by exposure to a relatively lowconcentration of monochloramine, the bacteria were able to present greater resistanceto inactivation during subsequent exposure to a relatively high concentration of thedisinfectant. This finding can contribute to the explanation of why M. avium cansurvive in drinking water distribution systems both in planktonic form and in biofilms.Accordingly, the objective of this study was to assess if an adaptive response occurredduring the sequential inactivation of M. avium with monochloramine. Materials and methods explained in the paper included: preparation of bacterial suspension; single-step disinfection; sequential disinfection; and, viability assessment. Includes 6 references, figures.

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Edition: Vol. - No. Published: 11/02/2003 Number of Pages: 7File Size: 1 file , 270 KB