Impacts of triclosan on stream microbial communities: investigating mitigation and multidrug resistance

Countless chemical compounds and their derivatives are present in wastewater (WW) systems and other environments due to anthropogenic inputs from a vast array of product ingredients. In streams and WW treatment plants (WWTPs), microbial communities thrive and can interact with these compounds in a variety of ways. Triclosan is an example of a synthetic chemical with expansive use which has, in half a century, become nearly ubiquitous in the environment. Investigating triclosan mitigation by periphyton from a WW-associated and a forested stream, the WW-associated periphyton showed evidence of mitigation. Similar triclosan levels were observed in both streams, in most samples of periphyton and water. Among water samples, higher triclosan concentrations were measured in samples collected nearest the WWTP. In microcosms, periphyton were exposed to an environmentally-relevant level (10 µg/L) of triclosan. Bacterial isolates were purified from the unexposed and triclosan exposed periphyton from each stream. Isolates were assayed for susceptibility to triclosan and five antibiotics using broth microdilution and identified to genus level via 16S rRNA sequence analysis. Pseudomonas was the dominant genus among identified isolates from all treatment groups and exposed groups had lower genus richness than unexposed. Multidrug-resistant (MDRt) bacteria were detected in both streams, with more incidences of multidrug resistance (MDR) in the WW-associated stream. The environmentally-relevant triclosan exposure appeared to increase antibiotic resistance and MDR in the forested-stream periphyton community but not the WW-associated community. Due to the growing global challenge of MDR, the added contribution of triclosan is a noteworthy risk to human and environmental health