Nonphotosynthetic pigmented bacteria in a potable water treatment and distribution system

Abstract

The occurrence of pigmented bacteria in potable water, from raw source water through treatment to distribution water, including dead-end locations, was compared at sample sites in a large municipal water system. Media used to enumerate heterotrophic bacteria and differentiate pigmented colonies were standard method plate count (SPC), m-SPC, and R2A agars, incubated up to 7 days at 35°C. The predominant pigmented bacteria at most sample locations were yellow and orange, with a small incidence of pink organisms at the flowing distribution site. Seasonal variations were seen, with the yellow and orange organisms shifting in dominance. SPC agar was the least productive medium for both heterotroph counts and pigmented bacteria differentiation. At the flowing distribution site, percentages of pigmented bacteria on SPC medium ranged from 2.3 to 9.67 times less than on m-SPC and from 2.3 to 9.86 times less than on R2A. At the same site, seasonal trends in the percentage of pigmented bacteria were the same for m-SPC and R2A media, and the highest and lowest percentages occurred in the fall and winter, respectively. At site 6, there appeared to be an inverse relationship between the yellow and orange pigmented groups, but upon analysis, this did not hold and all correlations between yellow and orange pigmented bacteria were positive. The study results indicate that pigmented bacteria could readily be detected by using plate counting media developed for heterotroph enumeration in potable waters with incubation periods of 7 days. Pigmented bacteria can be used as an additional marker for monitoring changes in water quality. High numbers of heterotrophs, including pigmented forms, were found at dead-end locations, usually in the absence of a free chlorine residual and when the water temperature was greater than 16°C. The association of some pigmented bacteria with nosocomial and other infections raises concern that the organisms may have originated from the potable water supply. High levels of pigmented bacteria could pose an increased health risk to immunologically compromised individuals. Therefore, the bacterial quality of the distribution water should be controlled to prevent the development of high concentrations of heterotrophic plate count bacteria, including the pigmented forms.