Comparative performance of colisureTM and accepted methods in the detection of chlorine-injured total coliforms and E. coli

Abstract

Studies were done to examine the comparability of ColisureTM and accepted reference methods to detect low numbers of total coliform bacteria and E. coli subjected to chlorine stress. ColisureTM is a medium designed to concurrently detect coliform bacteria and E. coli in drinking water by the specific action of β-galactosidase (total coliforms) and β-glucuronidase (E. coli). The methods used to compare the performance of various media followed a protocol established by the USEPA. Samples (31) of sewage from six different regions of the US were treated with sufficient concentrations of chlorine (1.2-2.5mg/l) to reduce viability 1-3 logs (39% average injury) and diluted with drinking water to achieve ca. 3 viable coliforms/100ml. The mean log reductions in viable bacteria, determined with various media following disinfection of the 31 samples were: mEndo = 1.87 (TC), ColisureTM = 1.55 (TC), mTec = 3.63 (E. coli) and ColisureTM = 2.01 (E. coli). When ColisureTM was compared with accepted methods to detect total coliforms in the dilute, disinfected samples, ColisureTM yielded results that were 1.6 times greater than LTB confirmed in BGLB at 28h. ColisureTM also detected 1.7 times greater levels of E. coli than LTB confirmed in EC/MUG at 28h. Sensitivity and specificity of ColisureTM were between 96 and 100% when positive and negative tests were verified. These findings indicate that ColisureTM is superior to certain accepted reference methods in the detection of chlorine-injured coliforms and E. coli under conditions that resemble contaminated drinking water.