Abstract
Heterotrophic plate count (HPC) is considered a useful general indicator of water quality. However, the analysis time is too long (48-72h) to provide information about a decrease in water quality that may require immediate remedial measures. High numbers of heterotrophic bacteria (HB) may also interact in the analysis of coliform bacteria resulting in false low numbers. Limited information is available on the variation of cellular 4-methylumbelliferyl-heptanoate hydrolase (MUHase) activity of HB under different environmental conditions and it is not known if MUHase activity exists in all HB. In this study, MUHase activity has been evaluated for rapid (25min) detection of HPC. The MUHase activity of different bacterial isolates from environmental water samples varied by several log units. Natural water samples showed less variation in activity calculated per CFU, indicating a relatively constant ratio between numbers of bacteria with high and low enzyme levels. The MUHase activity therefore provided a rapid estimate of the HPC of the water samples. The MUHase activity was more resistant to chlorine than the HPC, and separate HPC versus MUHase activity correlation curves should be established for chlorinated and non-chlorinated water.
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