The Impacts of Triclosan on Anaerobic Community Structures, Function, and Antimicrobial Resistance

Abstract

Triclosan is a widespread antimicrobial agent that accumulates in anaerobic digesters used to treat the residual solids generated at municipal wastewater treatment plants; there is very little information, however, about how triclosan impacts microbial communities in anaerobic digesters. We investigated how triclosan impacts the community structure, function and antimicrobial resistance genes in lab-scale anaerobic digesters. Previously exposed (to triclosan) communities were amended with 5, 50, and 500 mg/kg of triclosan, corresponding to the median, 95th percentile, and 4-fold higher than maximum triclosan concentration that has been detected in U.S. biosolids. Triclosan amendment caused all of the Bacteria and Archaea communities to structurally diverge from that of the control cultures (based on ARISA). At the end of the experiment, all triclosan-amended Archaea communities had diverged from the control communities, regardless of the triclosan concentration added. In contrast, over time the Bacteria communities that were amended with lower concentrations of triclosan (5 mg/kg and 50 mg/kg) initially diverged and then reconverged with the control community structure. Methane production at 500 mg/kg was nearly half the methane production in control cultures. At 50 mg/kg, a large variability in methane production was observed, suggesting that 50 mg/kg may be a tipping point where function begins to fail in some communities. When previously unexposed communities were exposed to 500 mg triclosan/kg, function was maintained, but the abundance of a gene encoding for triclosan resistance (mexB) increased. This research suggests that triclosan could inhibit methane production in anaerobic digesters if concentrations were to increase and may also select for resistant Bacteria. In both cases, microbial community composition and exposure history alter the influence of triclosan.

Sorption and degradation of triclosan in sediments and its effect on microbes

“…Following TCS addition, inhibition of microbial respiration in a sandy soil was reported (Waller and Kookana, 2009), and alteration of the fungal to bacterial ratio was also observed in soils (Butler et al, 2012). In anaerobic digesters, TCS amendment decreased the methane production and selected resistant bacteria (McNamara et al, 2014). However, effects of TCS on microbes in sediments have not been well characterized.…”

Anaerobic Membrane Bioreactor Effluent Reuse: A Review of Microbial Safety Concerns

“…Results from these works have shown variable results. For example, mexB genes, which confer multidrug efflux pump-based resistance, increased in mesophilic anaerobic digesters at high triclosan concentrations, while intl1 abundances decreased [61]. Triclocarban, a related antimicrobial, also increased mexB gene levels under similar conditions, while simultaneously reducing ermF genes [62].…”

Chronic exposure to triclosan sustains microbial community shifts and alters antibiotic resistance gene levels in anaerobic digesters

“…For example, cross-resistance to chloramphenicol developed from TCS exposure has been observed for E. coli, 13 P. aeruginosa, 14 S. maltophilia, 15 and S. enterica. 25 Previous research demonstrated that TCS can select for mexB, a component of a multidrug efflux pump, in mixed anaerobic communities seeded with manure, but no research describes the impact of long-term chronic exposure to TCS in anaerobic communities seeded with municipal anaerobic digester sludge. It has further been linked to resistance in bacteria found in pipes, sinks, wastewater treatment effluent, activated sludge, anaerobic digestion, and streams.…”

“…16,17 TCS is widely detected in the environment and ubiquitous in wastewater treatment plants. 25 The objective of this study was to determine if long-term TCS exposure resulted in sustained increases in relative abundance of antibiotic resistance genes (ARGs) and altered microbial community structure. [18][19][20][21] The majority of TCS entering a treatment plant sorbs to solids and passes through anaerobic digestion.…”