Triclosan resistant bacteria in sewage effluent and cross-resistance to antibiotics

The purpose of this study was to identify triclosan tolerant heterotrophic plate count (HPC) bacteria from sewage effluent and to determine cross-resistance to antibiotics. R2 agar supplemented with triclosan was utilised to isolate triclosan resistant bacteria and 16S rRNA gene sequencing was conducted to identify the isolates. Minimum inhibitory concentrations (MICs) of organisms were determined at selected concentrations of triclosan and cross-resistance to various antibiotics was performed. High-performance liquid chromatography was conducted to quantify levels of triclosan in sewage water. Forty-four HPC were isolated and identified as the five main genera, namely, Bacillus, Pseudomonas, Enterococcus, Brevibacillus and Paenibacillus. MIC values of these isolates ranged from 0.125 mg/L to >1 mg/L of triclosan, while combination of antimicrobials indicated synergism or antagonism. Levels of triclosan within the wastewater treatment plant (WWTP) ranged between 0.026 and 1.488 ppb. Triclosan concentrations were reduced by the WWTP, but small concentrations enter receiving freshwater bodies. Results presented indicate that these levels are sufficient to maintain triclosan resistant bacteria under controlled conditions. Further studies are thus needed into the impact of this scenario on such natural receiving water bodies.