Evaluation of the effectiveness of a commercially available defined substrate medium and enumeration system for measuring Escherichia coli numbers in faeces and soil samples*

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Abstract
To determine if a commercially available defined substrate medium and enumeration system could be utilized as an effective and accurate means of enumerating Escherichia coli in environmental samples containing faeces and soil. The samples tested were either inoculated with laboratory grown E. coli or natural E. coli populations in cow faeces. The number of E. coli recovered from faeces and soil samples using the defined substrate medium and enumeration system and a miniaturized MPN method (using traditional media) was compared by analysing the difference between the two methods in relation to the mean. For four of five groups of samples analysed there was no significant difference in the number of E. coli recovered by the two methods (P > 0.05). In one batch the difference was 0.30 log, which while being statistically significant (P < 0.01) was not considered to be biologically significant. The commercially available enumeration system was significantly more precise than the miniaturized MPN method (P < 0.001). We conclude that the commercially available defined substrate medium and enumeration system is a suitable method for the measurement of E. coli numbers in faeces and soil samples and should provide advantages of increased precision and a reduction in laboratory analysis time.