MI Agar for the Simultaneous Detection of Total Coliforms and Escherichia Coli in Environmental Waters

Total coliforms and Escherichia coli are the most important microbial indicators of fecal pollution. The traditional methods, such as the multiple-tube fermentation (MTF) technique and membrane-filter (MF) technique do not meet the requirements for fast and accurate testing. Recently, Defined Substrate Technology (DST) was developed to replace the traditional methods but it is a costly method and therefore, unpopular. A new membrane filter medium, MI agar, which was developed to simultaneously detect total coliforms and Escherichia coli in environmental water samples has been researched and is presented here. MI agar was compared with Endo agar, which was adopted by national standards. Spiked drinking water samples and real water samples were analyzed with duplicates by using MI agar-membrane filteration and Endo agar-membrane filteration. The results show that the average recovery rates by using MI agar method for total coliforms and Escherichia coli are 89.2% and 88.8% respectively, comparing favourably with the Endo agar method which has lower recovery rates of 81.0% and 81.2%. Thirty surface water samples were studied by using MI agar and Endo agar and the results show that there is no statistically significant difference between the two methods. The correlation coefficients by using MI agar method and Endo agar method were 0.9627 and 0.9511 for total coliforms and Escherichia coli, respectively. In summary, compared with national standards, MI agar is more sensitive, simpler to manage, less time consuming, has reduced interference effects and is suitable for the simultaneous detection of total coliforms and Escherichia coli. Since the results of this study show MI agar to be better than the current method, it meets the criteria for routine compliance monitoring of environmental water.