The potential for replication and transmission of antibiotic resistance plasmids in an E. coli population in agriculturally impacted stream sediment

The use of antibiotics in agriculture is thought to be a major cause of resistance in microorganisms found in the environment. Horizontal transfer of genetic information from transient to native and from native to transient bacterial populations may enhance the spread and recombination of resistance genes and might play a role in the formation of multi-resistant organisms in environmental reservoirs. Tetracycline resistance plasmids were compared using three isolation techniques -- traditional “endogenous” extraction from isolates, “exogenous” plasmid capture, and direct plasmid extraction from sediment --to determine the potential for plasmid born resistance in an E. coli population found in agriculturally-impacted stream sediment. Comparison of the number of tetracycline resistant E. coli in the sediment versus the water column identified the sediment as a more likely reservoir for resistance plasmids and therefore of genetic exchange. Exogenously captured, self-transmissible plasmids had a significantly greater incidence of resistance to multiple antibiotics than the endogenously isolated plasmids. Variation in plasmid extraction techniques eliminated some of the prejudice against the uncultivable environmental organisms and gave a more complete picture of the “mobilome” of tetracycline resistance plasmids that may circulate in populations of E. coli in stream sediments