Environmental and Water Studies, Dept. Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, USA.
Water Res. 2013 Nov 15;47(18):6849-61. doi: 10.1016/j.watres.2013.02.058. Epub 2013 Jul 11.
Fecal pollution is measured in surface waters using culture-based measurements of enterococci and Escherichia coli bacteria. Source apportionment of these two fecal indicator bacteria is an urgent need for prioritizing remediation efforts and quantifying health risks associated with source-specific pathogens. There are a number of quantitative real-time PCR (QPCR) assays that estimate concentrations of source-associated genetic markers; however, their concentrations are not necessarily amenable to source apportionment because the markers may differ in prevalence across sources. Here we mathematically derive and test, under ideal conditions, a method that utilizes the ratios of fecal source-associated genetic markers and culture and molecular measurements of general fecal indicators to apportion enterococci and E. coli. The source contribution is approximately equal to the ratio of the source-associated and the general fecal indicator concentrations in a water sample divided by their ratio in the source material, so long as cross-reactivity is negligible. We illustrate the utility of the ratio method using samples consisting of mixtures of various fecal pollution sources. The results from the ratio method correlated well with the actual source apportionment in artificial samples. However, aging of contamination can confound source allocation predictions. In particular, culturable enterococci and E. coli, the organisms presently regulated in the United States and much of the world, decay at different rates compared to source-associated markers and as a result cannot be apportioned using this method. However, limited data suggest a similar decay rate between source-associated and QPCR-measured Enterococcus and E. coli genetic markers, indicating that apportionment may be possible for these organisms; however further work is needed to confirm.
粪便污染是通过基于培养的肠球菌和大肠杆菌细菌测量来测量地表水的。这两种粪便指示菌的来源分配是当务之急，这需要优先进行修复工作，并量化与特定来源病原体相关的健康风险。有许多定量实时 PCR（QPCR）检测方法可以估算与来源相关的遗传标记的浓度；但是，它们的浓度不一定适合进行来源分配，因为标记在来源之间的流行率可能有所不同。在这里，我们在理想条件下推导出并测试了一种利用粪便来源相关遗传标记与培养和分子测量的一般粪便指示物的比率来分配肠球菌和大肠杆菌的方法。只要交叉反应可以忽略不计，那么在水样中，来源贡献大约等于水样中来源相关的和一般粪便指示物的浓度与来源材料中两者的浓度之比。我们使用由各种粪便污染来源组成的混合物的样本来说明比率法的实用性。比率法的结果与人工样本中的实际来源分配非常吻合。但是，污染的老化会使来源分配预测变得复杂。特别是，可培养的肠球菌和大肠杆菌，是目前在美国和世界上大部分地区受到监管的生物，与来源相关的标记相比，它们的衰减速度不同，因此不能使用这种方法进行分配。然而，有限的数据表明，来源相关和 QPCR 测量的肠球菌和大肠杆菌遗传标记之间存在相似的衰减率，这表明可能可以对这些生物进行分配；但是，还需要进一步的工作来确认。
