MI琼脂法同时检测环境水样中总大肠菌群和大肠埃希氏菌

总大肠菌群和大肠埃希氏菌是表征环境水样中粪便污染的两个重要指标。对这两个指标的检测,传统的多管发酵法和滤膜法已经无法满足快速、准确的检测要求。而近年来能够快速测定的固定酶底物技术(DST)已经在国内开始运用,但是由于其检测成本较高,影响了其在基层实验室的推广,MI琼脂法的出现较好地弥补了这个缺陷。本文应用MI琼脂法检测环境水样中总大肠菌群和大肠埃希氏菌,对其方法性能进行了测试和研究,选择国家标准方法——远藤琼脂法作为比较对象,通过菌种加标回收试验比较MI琼脂法和远藤琼脂法的灵敏度差异,通过实际水样的检测验证MI琼脂法和国标法是否具有等效性。结果表明:使用MI琼脂法检测总大肠菌群和大肠埃希氏菌加标样品的平均回收率分别为89.2%和88.8%,分别高于远藤琼脂法的81.0%和81.2%,证明MI琼脂法的灵敏度高于远藤琼脂法。MI琼脂法和远藤琼脂法检测总大肠菌群和大肠埃希氏菌的相关系数分别为0.9627和0.9511,都具有显著相关性,且检测结果没有统计学意义上的差异,证明两种方法检测总大肠菌群和大肠埃希氏菌具有等效性。与国家标准方法相比,MI琼脂法具有灵敏度高、操作简便、检测周期短、检测成本低、可同时检测两个指标等优点,可以替代传统的滤膜法作为检测总大肠菌群和大肠埃希氏菌的新方法。

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.