DETECTION OF ESCHERICHIA COLI IN WASTEWATER EFFLUENT USING M-COLIBLUE24®

Recently, there has been a trend towards using ESCHERICHIA COLI to monitor the quality of final effluent prior to discharge into the environment. A membrane filtration method, m-ColiBlue24®, was developed by Hach Company to detect total coliform bacteria while specifically differentiating E. coli present in water samples. Using m-ColiBlue24®, E. coli are differentiated from other total coliform bacteria based on the formation of a blue colored colony after incubation. The purpose of this work was to determine if m-ColiBlue24® could be used as a suitable alternative for detecting the presence of E. coli in wastewater samples. The first goal was to evaluate the recovery of E. coli from wastewater samples by comparing m-ColiBlue24® to two different standard membrane filtration media typically used for wastewater analysis. Another goal was to demonstrate effective detection of E. coli in wastewater samples in the presence of background total coliform bacteria. Finally, a third goal was to compare the recovery of E. coli from wastewater samples using two different formats of m-ColiBlue24®, a broth and an agar format. Initial comparative analyses were conducted over a five-month period of time at a municipal wastewater treatment facility. For these experiments, m-ColiBlue24® broth was compared to both m-TEC agar and m-FC broth. A total of 59 final effluent samples were collected, dechlorinated using sodium thiosulfate, and split into 100 ml portions which were filtered through 0.45 μm membrane filters using standard membrane filtration techniques. After the appropriate incubation period, bacterial colonies were counted, and the subsequent data was analyzed using the student's t-test. Results from these experiments showed no significant difference (p = 0.05) between m-ColiBlue24®, m-TEC agar, and m-FC broth in detecting the presence of E. coli in final wastewater effluent samples. In addition, blue colored E. coli colonies were easily observed and counted in the presence of greater than 300, non-E. coli, total coliform colonies. Additional comparative analyses were performed at another municipal wastewater treatment facility in a different geographical location. For this work, over a period of two separate months, 22 and 19 final effluent samples were collected, and processed as described above. For each sample, m-ColiBlue24® broth and agar formats were both compared to m-FC broth. Again, the student's t-test was used to compare the results, and no significant difference (p = 0.05) was observed in the detection of E. coli when using m-ColiBlue24® broth as compared to m-FC broth. However, while no significant difference (p = 0.05) was observed between m- ColiBlue24® agar and m-FC broth during the initial round of experiments, significantly more E. coli were detected using m-ColiBlue24® agar as compared to m-FC broth during a subsequent set of experiments. Therefore, m-ColiBlue24® is a rapid, reliable membrane filtration method that detects the presence of E. coli, and can be used to monitor the quality of final wastewater effluent.