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

Abstract

Studies were done to examine the comparability of Colisure™ and accepted reference methods to detect low numbers of total coliform bacteria and E.coli subjected to chlorine stress. Colisure™ is a medium designed to concurrently detect coliform bacteria and E.coli in drinking water by the specific action of ß-galactosidase (total coliforms) and ß-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 cohforms/100ml. The mean log reductions in viable bacteria, determined with various media following disinfection of the 31 samples were: mEndo = 1.87 (TC), Colisure™ = 1.55 (TC), mTec = 3.63 (E.coli) and Colisure™ = 2.01 (E.coli). When Colisure™ was compared with accepted methods to detect total coliforms in the dilute, disinfected samples. Colisure™ yielded results that were 1.6 times greater than LTB confirmed in BGLB at 28h. Colisure™ also detected 1.7 times greater levels of E.coli than LTB confirmed in EC/MUG at 28h. Sensitivity and specificity of Colisure™ were between 96 and 100% when positive and negative tests were verified. These findings indicate that Colisure™ is superior to certain accepted reference methods in the detection of chlorine-injured coliforms and E.coli under conditions that resemble contaminated drinking water.