Eccles J P, Searle R, Holt D, Dennis P J
Thames Water, Development Microbiology Laboratories, Spencer House, Reading, Berkshire, UK.
J Appl Microbiol. 2004;96(2):375-83. doi: 10.1046/j.1365-2672.2004.02165.x.
This study examined the suitability of three analytical methods for isolating and enumerating Escherichia coli from conventionally treated sewage sludge.
Crude sewage, mesophilic anaerobic digested (MAD) sludge, and final product sludge samples were taken from six sewage treatment works for analysis. Two of the three methods tested were membrane filtration techniques, utilizing chromogenic E. coli/coliform (CEC) media and membrane-lactose glucuronide agar (MLGA); the third method was a most probable number (MPN) technique utilizing Colilert in Quantitray 2000 (Idexx). The methods were evaluated for variation, consistency, false-positive and false-negative results, as well as method correlation. The methods gave good and consistent recovery of E. coli for a range of conventionally treated sewage matrices. All of the methods had a false-positive rate of <3%, although MLGA had a high false-negative rate (35.5%) compared with Colilert (3.81%) and the CEC method (6.75%). This resulted in slightly lower presumptive counts but comparable numbers of confirmed counts.
The three detection methods tested, chromogenic, MLGA and Colilert gave comparable recoveries, and did not vary by greater than one order of magnitude (1 log).
Forthcoming revisions to the Use of Sludge in Agriculture Regulations (1989) will categorize sewage sludge as untreated, conventionally treated or enhanced treated in accordance to microbiological standards. The standard will be based upon numbers of E. coli removed through the sludge treatment process and the numbers remaining in the final product. It is recommended that the Colilert 2000 (Idexx, Westbrook, Maine) and CEC methods would be equally suitable to assess the reduction of indigenous E. coli in conventionally treated sludges, and that MLGA be used with follow-up confirmatory testing.
本研究考察了三种分析方法用于从常规处理的污水污泥中分离和计数大肠杆菌的适用性。
从六个污水处理厂采集原污水、中温厌氧消化（MAD）污泥和最终产物污泥样本进行分析。所测试的三种方法中有两种是膜过滤技术，分别使用显色大肠杆菌/大肠菌群（CEC）培养基和膜乳糖葡糖醛酸琼脂（MLGA）；第三种方法是使用Quantitray 2000（Idexx）中的Colilert的最可能数（MPN）技术。对这些方法在变异性、一致性、假阳性和假阴性结果以及方法相关性方面进行了评估。对于一系列常规处理的污水基质，这些方法对大肠杆菌的回收率良好且一致。所有方法的假阳性率均<3%，不过与Colilert（3.81%）和CEC方法（6.75%）相比，MLGA的假阴性率较高（35.5%）。这导致推测计数略低，但确认计数数量相当。
所测试的三种检测方法，即显色法、MLGA和Colilert，回收率相当，且差异不超过一个数量级（1 log）。
即将修订的《农业污泥使用规定》（1989年）将根据微生物标准将污水污泥分类为未处理、常规处理或强化处理。该标准将基于通过污泥处理过程去除的大肠杆菌数量以及最终产物中残留的数量。建议Colilert 2000（Idexx，缅因州韦斯特布鲁克）和CEC方法同样适用于评估常规处理污泥中本地大肠杆菌的减少情况，并且MLGA应与后续的确认性检测一起使用。
