Evaluation of Colilert-18 for the detection of coliforms and Escherichia coli in tropical fresh water.

Aims: To evaluate the suitability of Colilert-18 in detecting Escherichia coli and total coliforms in tropical freshwater samples. Methods and Results: Target organisms were isolated from yellow-fluorescent and yellow wells of Colilert-18/Quanti-Tray using m-TEC agar and m-ENDO LES agar respectively. All the selected isolates were first identified based on their fatty acid methyl ester profile. Isolates showing contradictory results to that of the Colilert-18 procedure were re-identified using API 20E strips. A total of 357 isolates, 177 from yellow-fluorescent wells and 180 from yellow wells, were identified. Conclusions: The false-positive and -negative rates for E. coli detection using Colilert-18 were 36·4% and 11%, respectively, while for coliform detection the false-positive rate was 10·3%. Significance and Impact of the Study: The high false-positive rate of Colilert-18, tempers its value for E. coli detection when used for tropical freshwater samples. [ABSTRACT FROM AUTHOR]