Enumeration of Escherichia coli and coliforms in surface water by multiple tube fermentation and membrane filter methods

The current investigation was carried out in order to compare directly the multiple tube fermentation method (MTF), using standard procedures (lactose broth, LB) and the Colilert reagent, with the membrane filter method (MF) using Les Endo agar (LEA), m-faecal coliform agar (mFCA) and chromogenic coliform agar (CCA), for recovery of coliforms and Escherichia coli in 80 surface water samples. Total coliforms were isolated from 100% of samples by all methodologies. Faecal coliforms/E. coli were detected in 100% of samples by MTF methods, but only in 75.5% by MF-mFCA and in 86.2% by MF-CCA. Even if MTF-LB counts were consistently higher, the Colilert reagent accurately determined total coliforms and E. coli levels within 24 h with no additional confirmatory tests. Therefore, it could be a powerful tool for rapidly assessing possible faecal contamination and a suitable alternative to the traditional MTF and MF techniques utilized for coliform detection.