AWWA WQTC58790 Comparison of Five Commercially Available Methods for Detection of Coliforms and E.coli

Conference Proceeding by American Water Works Association, 11/02/2003

Fricker, Colin; Warden, Paul; Silvaggio, Daniel; Glesseman, Erica; Tamanaha, Roy; Rust, Jan; Eldred, Bradley

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This paper compares five methods for the detection of coliforms and E.coli in water. Thestudy was performed in two parts, one specifically to examine the specificity of themethods, particularly with regard to Aeromonas spp., and the otherinvestigating the sensitivity, particularly with regard to E.coli. Considerabledifferences were seen between some of the methods. Colitag (CPI, CA) was foundto be extremely non-specific, giving high numbers of false positives when Aeromonaswas present in the water. This occurred even at low levels of Aeromonas (10cfu/ml) in some samples. The remaining media were generally fairly specific,although all media produced occasional false positive coliform results. ReadyCult(Merck) gave increased numbers of false positive coliform results when it wasincubated for 29 h, but this length of incubation was required to facilitate acceptablelevels of E.coli detection. Occasional false positive E.coli results were seen withReadyCult apparently due to the presence of fluorescent pseudomonads.Furthermore, the size of vessel used for incubation affected the ReadyCult result.When incubated in vessels of 120 ml volume, some samples which containedcoliforms and/or E.coli failed to give a positive coliform reaction. In these situations,the reaction was weak but detectable in 150 ml vessels and clearly detectable in 250ml vessels. Removing the lid from 120 ml vessels and leaving the sample on thebench for 10-30 minutes allowed color to develop. Colilert 18 (IDEXX, ME) wasthe most specific and most sensitive of the five methods tested. Includes tables.

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Edition: Vol. - No. Published: 11/02/2003 Number of Pages: 6 File Size: 1 file , 240 KB