Enumeration and characterization of standard plate count bacteria in chlorinated and raw water supplies

Abstract

Nearly 700 standard plate count (SPC) bacteria were isolated from drinking water and untreated surface water and identified according to a scheme developed to permit the rapid, simple classification of microorganisms to genus, species or group. Actinomycetes and Aeromonas spp. were the 2 most common groups of SPC bacteria in chlorinated distribution water. Aeromonas spp. and Enterobacter agglomerans were the 2 most common groups of SPC bacteria in raw water. Identification of bacterial populations before and after contact with Cl (1-2 mg/l) for 1 h revealed that chlorination selected for gram-positive bacteria. Water that contained high densities of bacteria known to be antagonistic to coliforms had low coliform isolation rates. The membrane filtration technique for enumerating SPC bacteria recovered significantly higher numbers (P < 0.001) than the standard pour plate technique.