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

Studies were done to examine the comparability of Colisure^TM and accepted reference methods to detect low numbers of total coliform bacteria and E. coli subjected to chlorine stress. Colisure^TM 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), Colisure^TM = 1.55 (TC), mTec = 3.63 (E. coli) and Colisure^TM = 2.01 (E. coli). When Colisure^TM was compared with accepted methods to detect total coliforms in the dilute, disinfected samples, Colisure^TM yielded results that were 1.6 times greater than LTB confirmed in BGLB at 28h. Colisure^TM also detected 1.7 times greater levels of E. coli than LTB confirmed in EC/MUG at 28h. Sensitivity and specificity of Colisure^TM were between 96 and 100% when positive and negative tests were verified. These findings indicate that Colisure^TM is superior to certain accepted reference methods in the detection of chlorine-injured coliforms and E. coli under conditions that resemble contaminated drinking water.