William J. Staddon
Wastewater treatment plants appear to play a role in releasing antimicrobial compounds and resistant genes into the environment. The phenomenon of bacterial resistance to multiple antimicrobial compounds is not well understood with regards to public health. Studies have examined cross-resistance to triclosan and various antibiotics in bacteria. These resistance mechanisms: target site modification, membrane resistance, and efflux pumps indicate possible ways in which bacteria have adapted to antibiotics as well as triclosan. In addition, antibiotic resistance genes occur naturally in the environment and are passed from species to species through horizontal gene transfer. Sediment samples were collected from above and below the Town Branch wastewater treatment plant in Lexington, KY. Bacteria capable of growing in the presence of triclosan were subcultured on media containing antibiotics. Isolates were then identified through sequencing of the 16S rRNA. The three most prevalent genera identified were Pseudomonas, Enterobacter, and Bacillus. All of the isolates were resistant to β-lactams and several other antibiotics. Moreover, all of the isolates were sensitive to tetracycline, doxycycline, and ciprofloxacin. Therefore, isolates potentially exhibit cross-resistance to triclosan and various antibiotics. Efflux pumps are a mechanism that may allow these isolates to target triclosan and antibiotics by pumping them out across the cell membrane back into the environment. However, the impact of triclosan on the spread of antibiotic resistance genes in the environment is not well understood. Therefore, the relevance of this co-resistance remains unclear.
Keywords: wastewater treatment plants, triclosan, cross-resistance, antibiotic resistance genes