Rapid enzymatic detection of heterotrophic activity of environmental bacteria

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 re medial measures. High numbers of heterotrophic bacteria (HB) may also inter act in the analysis of coliform bacteria resulting in false low numbers. Li mited information is available on the variation of cellular 4-methylumbelli feryl-heptanoate hydrolase (MUHase) activity of HE under different environm ental conditions and it is not known if MUHase activity exists in all HE. I n this study, MUHase activity has been evaluated for rapid (25min) detectio n of HPC. The MUHase activity of different bacterial isolates from environm ental water samples varied by several log units. Natural water samples show ed less variation in activity calculated per CFU, indicating a relatively c onstant ratio between numbers of bacteria with high and low enzyme levels. The MUHase activity therefore provided a rapid estimate of the HPC of the w ater samples. The MUHase activity was more resistant to chlorine than the H PC, and separate HPC versus MUHase activity correlation curves should be es tablished for chlorinated and non-chlorinated water. (C) 1998 IAWQ Publishe d by Elsevier Science Ltd. All rights reserved.