Chlorine, Chloramine, Chlorine Dioxide, and Ozone Susceptibility of Mycobacterium avium

Abstract

Environmental and patient isolates of Mycobacterium avium were resistant to chlorine, monochloramine, chlorine dioxide, and ozone. For chlorine, the product of the disinfectant concentration (in parts per million) and the time (in minutes) to 99.9% inactivation for five M. avium strains ranged from 51 to 204. Chlorine susceptibility of cells was the same in washed cultures containing aggregates and in reduced aggregate fractions lacking aggregates. Cells of the more slowly growing strains were more resistant to chlorine than were cells of the more rapidly growing strains. Water-grown cells were 10-fold more resistant than medium-grown cells. Disinfectant resistance may be one factor promoting the persistence of M. avium in drinking water.Mycobacterium avium is an environmental, opportunistic human pathogen (8,25) that infects between 25 and 50% of advanced-stage AIDS patients in the United States (15). M. avium has been isolated from drinking water and municipal water systems (6,9,10,12,14,23) and grows in water (11). M. avium isolates recovered from municipal water systems and local natural water sources have the same DNA fingerprints as those recovered from AIDS patients exposed to the water (24). One reason for the persistence of M. avium in drinking water could be resistance to disinfection methods (e.g., chlorination). A number of environmental, opportunistic mycobacteria, including M. avium, have been shown to be relatively resistant to chlorine or chloramine at concentrations used in municipal water systems for disinfection (3,4,7,14,19,20,21). Unfortunately, those earlier studies were flawed because strains were not completely identified, different colony types were used, cells were grown on different media and to different stages, and aggregates were not excluded from the cell suspensions. Most mycobacterial species, including M. avium, form aggregates or clumps during growth in media (16,18), and the presence of aggregates can lead to spurious disinfection resistance (22) and variable colony counts due to irregular dispersal of aggregates. The objective of the studies described here was to develop a method to produce M. avium cell suspensions lacking large aggregates and to compare the susceptibility of medium-and water-grown M. avium suspensions to chlorine, monochloramine, chlorine dioxide, and ozone.The M. avium strains A5 (1), 1508, 1060, 5002, and 5502 (24) were identified by DNA probe (Gen-Probe, San Diego, Calif.). M. avium strain A5 was isolated from an AIDS patient and was received from Marjorie Beggs McClellan Veterans Hospital, Little Rock, Ark. Because A5 was not isolated by Marjorie Beggs, it was undoubtedly subject to numerous transfers before receipt in the Virginia Tech laboratory. Its inclusion in this study is based on the fact that it is one of the few strains of M. avium that have been transformed. Thus, it can serve as a host for genes involved in chlorine resistance. In contrast, strains 1060, 1508, 5002, and 5502 were isolated as part of a study in which the Virginia Tech laborat...

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