Pour and spread plates are the conventional methods of choice for the isolation and enumeration of heterotrophic microorganisms in treated water supplies. The tests are performed at 22°C and 37°C for 72 h and 48 h respectively. Counts at 22°C are associated with pollution of water systems from external sources, while counts at 37°C are used as an indication of treatment plant performance and the deterioration of the general quality of water. Conventional methods using Yeast Extract Agar for a pour plate and R2A agar for a spread plate were compared with the multidose IDEXXTM SimPlate method for the isolation and enumeration of heterotrophic bacteria in water. SimPlate gave a significantly higher count on average than the conventional methods. The R2A method showed the next highest count, being significantly higher than Yeast Extract Agar. In addition, unlike the pour and spread plate methods, SimPlate was easier to use, reduced labour, and the test results were far easier to read.

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