P133: Dissemination of bacterial fluoroquinolone resistance in the wastewater treatment plant environment

Over 50 million pounds of antibiotics are produced every year and many of these antibiotics end up in waste streams or wastewater treatment plants (WWTP) around the world. Environmental exposure of bacteria to these antibiotics has led to recruitment of antibiotic resistance mechanisms. Although bacterial horizontal gene transfer is well documented, the mechanisms are not well understood. We have been interested in investigating and tracking the transfer of various mobile genetic elements from known bacterial hosts to naïve recipients. As a model for conjugal gene transfer, fluoroquinolone resistant bacteria were chosen as gene donors: Escherichia coli strain LR09, Escherichia coli strain N12406, and Enterobacter aerogenes QepA⁺, each representing a different resistance mechanism. WWTP sludge and effluent were also used to search for native antibiotic resistant organisms and as a bioreactor inoculum. The WWTP reactor liquor and final effluent were metagenomically screened and found to contain the FQ resistance gene aac(6’)-lb-cr while pure culture isolations yielded four colonies positive for aac(6’)-lb-cr and five for qnrB. Filter matings were conducted between donors and various recipients. Successful demonstration of at least one gene transfer event between E. aerogenes QepA⁺ and Klebsiella pneumoniae has been confirmed to date. To enable more efficient screening for transconjugants, the donor organisms were tagged with fluorescent genes. Currently plasmids containing the resistant genes are being fluorescently labeled. Microcosms containing donors and recipients have also been established and rates of gene transfer are being monitored.