Eight water distribution systems were sampled over an 18-month period (528 water and 55 biofilm samples) to measure the frequency of recovery and number of mycobacteria, particularly Mycobacterium avium and Mycobacterium intracellulare, in raw source waters before and after treatment and within the distribution system. The systems were chosen to assess the influence of source water, treatment, and assimilable organic carbon levels on mycobacterial numbers. Overall, mycobacterial recovery from the systems was low (15% of samples). Numbers of mycobacteria ranged from 10 to 700,000 CFU liter ؊1 . The number of M. avium in raw waters was correlated with turbidity. Water treatment substantially reduced the number of mycobacteria in raw waters by 2 to 4 log units. Mycobacterial numbers were substantially higher in the distribution system samples (average, 25,000-fold) than in those collected immediately downstream from the treatment facilities, indicating that mycobacteria grow in the distribution system. The increase in mycobacterial numbers was correlated with assimilable organic carbon and biodegradable organic carbon levels (r 2 ‫؍‬ 0.65, P ‫؍‬ 0.03). Although M. intracellulare was seldom recovered from water samples, it was frequently recovered (six of eight systems) in high numbers from biofilms (average, 600 CFU/cm 2 ). Evidently, the ecological niches of M. avium and M. intracellulare are distinct.Members of the Mycobacterium avium complex (i.e., M. avium and Mycobacterium intracellulare) are environmental opportunistic human and animal pathogens (11,21,43). M. avium complex pulmonary infections are found in patients with predisposing lung conditions, such as silicosis and black lung (5, 43), and in patients with pulmonary alveolar proteinosis (42) and cystic fibrosis (23). Infections in elderly women without any of the known risk factors for M. avium complex infection have also been described (30). M. avium, but not M. intracellulare, infections are found in (and are limited to) the cervical lymph nodes of young children with erupting teeth (44). Immune deficiency resulting in AIDS (18) or due to interleukin-12 deficiency (1), malignancy (41), or immunosuppression associated with transplantation (33) is also a risk factor for M. avium complex infection. Infections in AIDS patients are disseminated (e.g., bacteremia [19]) and are almost entirely (i.e., 95%) due to M. avium, whereas both mycobacterial infections occur at equal frequencies in nonimmunodeficient patients with pulmonary disease (8, 17).One source of M. avium infection in AIDS patients is water. DNA fingerprints of M. avium isolates from water to which AIDS patients were exposed were identical to those of the patients (38). Further, the high incidence of M. avium infections in AIDS patients in Finland correlated with high numbers of M. avium in drinking and environmental waters (31). Water also appears to be the source of M. avium infections in simian immunodeficiency virus-infected macaques, based on the identity of DNA fingerprints of M. avium re...

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...

An 18-month survey of 31 water systems in North America was conducted to determine the factors that contribute to the occurrence of coliform bacteria in drinking water. The survey included analysis of assimilable organic carbon (AOC), coliforms, disinfectant residuals, and operational parameters. Coliform bacteria were detected in 27.8% of the 2-week sampling periods and were associated with the following factors: filtration, temperature, disinfectant type and disinfectant level, AOC level, corrosion control, and operational characteristics. Four systems in the study that used unfiltered surface water accounted for 26.6% of the total number of bacterial samples collected but 64.3% (1,013 of 1,576) of the positive coliform samples. The occurrence of coliform bacteria was significantly higher when water temperatures were >15؇C. For filtered systems that used free chlorine, 0.97% of 33,196 samples contained coliform bacteria, while 0.51% of 35,159 samples from chloraminated systems contained coliform bacteria. The average density of coliform bacteria was 35 times higher in free-chlorinated systems than in chloraminated water (0.60 CFU/100 ml for free-chlorinated water compared with 0.017 CFU/100 ml for chloraminated water). Systems that maintained dead-end free chlorine levels of <0.2 mg/liter or monochloramine levels of <0.5 mg/liter had substantially more coliform occurrences than systems that maintained higher disinfectant residuals. Free-chlorinated systems with AOC levels greater than 100 g/liter had 82% more coliform-positive samples and 19 times higher coliform levels than freechlorinated systems with average AOC levels less than 99 g/liter. Systems that maintained a phosphate-based corrosion inhibitor and limited the amount of unlined cast iron pipe had fewer coliform bacteria. Several operational characteristics of the treatment process or the distribution system were also associated with increased rates of coliform occurrence. The study concludes that the occurrence of coliform bacteria within a distribution system is dependent upon a complex interaction of chemical, physical, operational, and engineering parameters. No one factor could account for all of the coliform occurrences, and one must consider all of the parameters described above in devising a solution to the regrowth problem.

Giardia and Cryptosporidium levels were determined by using a combined immunofluorescence test for source waters of 66 surface water treatment plants in 14 states and 1 Canadian province. The results showed that cysts and oocysts were widely dispersed in the aquatic environment. Giardia spp. were detected in 81% of the raw water samples. Cryptosporidium spp. were found in 87% of the raw water locations. Overall, Giardia or Cryptosporidium spp. were detected in 97% of the raw water samples. Higher cyst and oocyst densities were associated with source waters receiving industrial or sewage effluents. Significant correlations were found between Giardia and Cryptosporidium densities and raw water quality parameters such as turbidity and total and fecal coliform levels. Statistical modeling suggests that cyst and oocyst densities could be predicted on the basis of watershed and water quality characteristics. The occurrence of high levels of Giardia cysts in raw water samples may require water utilities to apply treatment beyond that outlined in the Surface Water Treatment Rule of the U.S. Environmental Protection Agency.

The current project was developed to examine inactivation of biofilm bacteria and to characterize the interaction of biocides with pipe surfaces. Unattached bacteria were quite susceptible to the variety of disinfectants tested. Viable bacterial counts were reduced 99% by exposure to 0.08 mg of hypochlorous acid (pH 7.0) per liter (1 to 2°C) for 1 min. For monochloramine, 94 mg/liter was required to kill 99% of the bacteria within 1 min. These results were consistent with those found by other investigators. Biofilm bacteria grown on the surfaces of granular activated carbon particles, metal coupons, or glass microscope slides were 150 to more than 3,000 times more resistant to hypochlorous acid (free chlorine, pH 7.0) than were unattached cells. In contrast, resistance of bioflim bacteria to monochloramine disinfection ranged from 2to 100-fold more than that of unattached cells. The results suggested that, relative to inactivation of unattached bacteria, monochloramine was better able to penetrate and kill biofilm bacteria than free chlorine. For free chlorine, the data indicated that transport of the disinfectant into the biofilm was a major rate-limiting factor. Because of this phenomenon, increasing the level of free chlorine did not increase disinfection efficiency. Experiments where equal weights of disinfectants were used suggested that the greater penetrating power of monochloramine compensated for its limited disinfection activity. These studies showed that monochloramine was as effective as free chlorine for inactivation of biofilm bacteria. The research provides important insights into strategies for control of biofilm bacteria.