Heterotrophic Bacteria in Chlorinated Drinking Water Distribution Systems: Detection and Identification

Abstract

In order to determine bacterial quality of supplied water, researches on detection and identification of heterotrophic bacteria In distribution basin water and tap water were conducted In several drinking water supply systems In Japan, using pour plate technique with two agar media of SPG (Incubated at 36°C) and PGY (at 25°C). Bacterial colonies formed on SPC agar were randomly selected, purified and identified to genus. Results obtained from this study were as follow. The density of SPC bacteria ranged from 0 to 190 cfu/mL, although no colony was detected after 1-day Incubation in all of water samples tested. The density of PGY bacteria was higher than SPC and were In the range of 0 to 380 cfu/mL. Maximal values were found In first flow of water from taps In the early morning which contained lower residual chlorine. Prolonged incubation time resulted In Increased bacterial counts on both SPC and PGY plates. This tendency was more noticeable In samples collected from taps, particularly In first flow of water In the early morning. Dominant genera of the bacteria grown on SPG varied with different water supply systems and were Alcaligenes, Bacillus, Flavobacterlum, Methylobacterlum and Pseudomonas.