Lasalde Clarivel, Rodríguez Roberto, Toranzos Gary A
Environmental Microbiology Laboratory, University of Puerto Rico Department of Biology, P.O. Box 23360, San Juan, PR.
Appl Environ Microbiol. 2005 Aug;71(8):4690-5. doi: 10.1128/AEM.71.8.4690-4695.2005.
Analyses for the presence of indicator organisms provide information on the microbiological quality of water. Indicator organisms recommended by the United States Environmental Protection Agency for monitoring the microbiological quality of water include Escherichia coli, a thermotolerant coliform found in the feces of warm-blooded animals. These bacteria can also be isolated from environmental sources such as the recreational and pristine waters of tropical rain forests in the absence of fecal contamination. In the present study, E. coli isolates were compared to E. coli K12 (ATCC 29425) by restriction fragment length polymorphism using pulsed-field gel electrophoresis. Theoretically, genomic DNA patterns generated by PFGE are highly specific for the different isolates of an organism and can be used to identify variability between environmental and fecal isolates. Our results indicate a different band pattern for almost every one of the E. coli isolates analyzed. Cluster analysis did not show any relations between isolates and their source of origin. Only the discriminant function analysis grouped the samples with the source of origin. The discrepancy observed between the cluster analysis and discriminant function analysis relies on their mathematical basis. Our validation analyses indicate the presence of an artifact (i.e., grouping of environmental versus fecal samples as a product of the statistical analyses used and not as a result of separation in terms of source of origin) in the classification results; therefore, the large genetic heterogeneity observed in these E. coli populations makes the grouping of isolates by source rather difficult, if not impossible.
对指示生物的分析可提供有关水微生物质量的信息。美国环境保护局推荐用于监测水微生物质量的指示生物包括大肠杆菌，它是一种在温血动物粪便中发现的耐热大肠菌群。在没有粪便污染的情况下，这些细菌也可从环境来源中分离出来，如热带雨林的休闲水域和原始水域。在本研究中，通过脉冲场凝胶电泳的限制性片段长度多态性，将大肠杆菌分离株与大肠杆菌K12（ATCC 29425）进行比较。理论上，PFGE产生的基因组DNA模式对生物体的不同分离株具有高度特异性，可用于识别环境分离株和粪便分离株之间的变异性。我们的结果表明，几乎每一个分析的大肠杆菌分离株都有不同的条带模式。聚类分析未显示分离株与其来源之间的任何关系。只有判别函数分析将样本按来源进行了分组。聚类分析和判别函数分析之间观察到的差异取决于它们的数学基础。我们的验证分析表明，分类结果中存在一种假象（即，将环境样本与粪便样本分组是所用统计分析的结果，而不是来源分离的结果）；因此，在这些大肠杆菌群体中观察到的大的遗传异质性使得按来源对分离株进行分组即使不是不可能，也是相当困难的。
