Analysis of Escherichia coli populations in a large watershed.
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Nemec, Michelle D.
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Escherichia coli are one of the most common model organisms used today. This organism has played an integral role in our understanding of bacterial conjugation, phage genetics, and gene structure, and it is also responsible for many of the advances in the areas of proteomics and biotechnology. However, very little is known about the characteristics of E. coli populations in their natural habitats. In this study, three characteristics of E. coli populations isolated from nine different sources were investigated, including: 1) antibiotic resistance, 2) carbon–substrate usage, and 3) genetic diversity. Antibiotic resistance was examined using eight antibiotics. Overall, the incidence of amoxicillin resistance was high in all of the E. coli populations, and multi-drug resistance was common. Antibiotic resistance was prevalent across populations, and the highest level of resistance was found in isolates obtained from sewage and dairy cattle. The carbon–substrate utilization of the E. coli populations was examined using Biolog GN2 microplates. The fundamental metabolic capabilities of the E. coli isolates were relatively stable across populations; however, variation did occur in the extent to which some isolates in the populations could utilize the various carbon substrates. Metabolic similarities were greatest between E. coli isolates from the same population. Rep–PCR was implemented to assess the genetic diversity present in the various E. coli populations. Overall, the genetic diversity of the E. coli isolates appeared to be large. Unfortunately, there are very few other studies available with which to compare these data. The level of genetic diversity varied between each population of isolates; although, isolates from the same population tended to be more genetically similar than isolates from different populations. Finally, Jackknife analysis demonstrated that the various E. coli populations were more distinct from each other genetically than they were based on antibiotic resistance or carbon–utilization. When all three characteristics were combined, relatively clear distinctions could be made between most populations. When the characteristics of E. coli isolated from water were compared with the characteristics of the isolates from the other sources, the majority of the water isolates were most similar to E. coli obtained from cattle.