Characterization of bacterial isolates from a shallow aquifer suspected to be contaminated by urban wastes

The El Paso-Juarez (Mexico) region is one of the most populated areas on the US-Mexico border with a combined population of about 2 million people. Due to the lack of waste water treatment facilities in Juarez and in certain locations of El Paso, there are serious concerns about microbial contamination of transboundary surface and groundwater resources. Groundwater samples were obtained from nineteen domestic wells close to the border and the bacterial isolates characterized using their genotypic and phenotypic properties to determine if they were of sewage origin. None of the samples showed the presence off. coli though other members of the Enterobacteriaceae were isolated. Genetic fingerprinting of the Enterobacter sp. indicate that there is no significant genetic similarity between the isolates from within a single well or different wells to suggest a common source for the organisms. Antibiotic resistance profiles suggests that the isolates are probably not of sewage origin. The results do not provide sufficient evidence to suggest that the microbial populations are originating from household and municipal waste streams which could be linked to a single source.