Nonstandard methods for enumerating bacteria in drinking water

Abstract

Various enumeration procedures were examined to determine the optimum conditions for maximizing viable counts of bacteria from drinking waters. Nonstandard procedures that increased bacterial count included (a) media that were more dilute than Standard Methods Agar, (b) incubation periods that ranged from 2 to 13 or 14 days and longer, and (c) an incubation temperature of 20°C. The differences between these results and those of other recent investigations suggest that there may be regional differences in bacterial flora which account for the differences in efficacy of enumeration procedures. In addition, strain diversity was estimated for heterotrophic bacteria from nonchlorinated and chlorinated waters. In this study, untreated source waters had greater diversity than did chlorinated samples. This preliminary evidence may indicate that chlorination allows few species to survive in distribution systems.