Genetic Diversity and Antimicrobial Resistance in Escherichia Coli Isolates in Constructed Wetlands Treating Swine Wastewater.

The treatment and the removal of contaminants such as nutrients, salts, microbes, and pharmaceutical active compounds from swine waste by constructed wetland involve complex biological processes.  However, little is known about the population structure and antimicrobial resistant phenotype/genotype of E. coli from the swine house through a surface flow constructed wetland that is used for the treatment and removal of some contaminants in the swine waste. To assess the impacts of seasonal variations and the mechanism of the wetland layout/operations on E. coli populations, we compared the genetic diversity and antimicrobial activities of the bacteria in a surface flow constructed wetlands used for treating swine waste. E. coli was enumerated and typed from samples collected from swine house (manure), influence or source water from the swine house, anaerobic storage lagoon, storage tank, surface flow constructed wetland environment, and the final effluence. Typing of E. coli was done using BOXAIR-1 and REP-PCR followed by antimicrobial activities. None of the isolates was confirmed as Shiga toxin E. coli O157:H7 (STEC), but as others, such as enterotoxigenic E. coli (ETEC). Using a 90% similarity index from the REP-PCR, 175 unique clones out of 422 were found. Our data showed that most of the E. coli strains were without the Shiga toxin genes, but with high distribution of resistant phenotypes. Therefore, the occurrence of E. coli with multiple resistances in the wetland is a matter of great concern due to possible transfer of resistant genes from nonpathogenic to pathogenic strains that may result in increased duration and severity of morbidity.