Casarez Elizabeth A, Pillai Suresh D, Di Giovanni George D
Texas Agricultural Experiment Station, Texas A&M University Agricultural Research Center, 1380 A&M Circle, El Paso, TX 79927, USA.
Water Res. 2007 Aug;41(16):3643-8. doi: 10.1016/j.watres.2007.03.020. Epub 2007 May 2.
Most library-dependent bacterial source tracking studies using Escherichia coli (E. coli) have focused on strain diversity of isolates obtained from known human and animal faecal sources for library development. In contrast, this study evaluated the genotype variation of E. coli isolated from natural surface water using pulsed field gel electrophoresis (PFGE) and enterobacterial repetitive intergenic consensus sequence polymerase chain reaction (ERIC-PCR) to better understand these naturally occurring populations. A total of 650 water samples were collected over a nine month period from eleven sampling stations from Lake Waco and Belton Lake in Central Texas. Of the 650 water samples collected, 412 were positive for E. coli, yielding a total of 631 E. coli isolates (1-12 isolates collected per sample). PFGE and ERIC-PCR patterns were successfully generated for 555 isolates and were compared using the curve-based Pearson's product-moment correlation coefficient. The 555 E. coli isolates represented 461 PFGE genotypes, with 84% (386/461) of the genotypes being represented by individual isolates. The remaining 75 genotypes were represented by 2-5 isolates each. Using ERIC-PCR, the 555 E. coli isolates represented 175 genotypes, with 63% (109/175) of the genotypes being represented by individual isolates. In contrast to the PFGE results, two ERIC-PCR genotypes represented 37% of the E. coli isolates, (83 and 124 isolates, respectively), and were found throughout the watersheds both spatially and temporally. Based on the PFGE genotype diversity of water isolates, there is little evidence that a small number of environmentally-adapted E. coli represent dominant populations in the studied waterbodies. However, with the lower discriminatory power technique ERIC-PCR, an opposing conclusion might have been drawn. These results emphasize the importance of considering the resolving power of the source tracking technique being used when assessing strain diversity and geographical stability.
大多数依赖文库的利用大肠杆菌（E. coli）进行的细菌源追踪研究都聚焦于从已知人类和动物粪便源获得的分离株的菌株多样性，用于构建文库。相比之下，本研究利用脉冲场凝胶电泳（PFGE）和肠杆菌重复基因间共有序列聚合酶链反应（ERIC-PCR）评估了从天然地表水分离的大肠杆菌的基因型变异，以更好地了解这些自然存在的菌群。在九个月的时间里，从德克萨斯州中部韦科湖和贝尔顿湖的11个采样站共采集了650份水样。在采集的650份水样中，412份大肠杆菌检测呈阳性，共获得631株大肠杆菌分离株（每份样品采集1 - 12株分离株）。成功生成了555株分离株的PFGE和ERIC-PCR图谱，并使用基于曲线的皮尔逊积矩相关系数进行比较。这555株大肠杆菌分离株代表了461种PFGE基因型，其中84%（386/461）的基因型由单个分离株代表。其余75种基因型分别由2 - 5株分离株代表。利用ERIC-PCR，这555株大肠杆菌分离株代表了175种基因型，其中63%（109/175）的基因型由单个分离株代表。与PFGE结果相反，两种ERIC-PCR基因型代表了37%的大肠杆菌分离株（分别为83株和124株），并且在整个流域的空间和时间上均有发现。基于水样分离株的PFGE基因型多样性，几乎没有证据表明少数适应环境的大肠杆菌在研究水体中代表优势菌群。然而，使用鉴别力较低的技术ERIC-PCR，可能会得出相反的结论。这些结果强调了在评估菌株多样性和地理稳定性时，考虑所使用的源追踪技术分辨能力的重要性。
