Exposure of Sink Drain Microcosms to Triclosan: Population Dynamics and Antimicrobial Susceptibility

Abstract

Recent concern that the increased use of triclosan (TCS) in consumer products may contribute to the emergence of antibiotic resistance has led us to examine the effects of TCS dosing on domestic-drain biofilm microcosms. TCS-containing domestic detergent (TCSD) markedly lowered biofouling at 50% (wt/vol) but was poorly effective at use levels. Long-term microcosms were established and stabilized for 6 months before one was subjected to successive 3-month exposures to TCSD at sublethal concentrations (0.2 and 0.4% [wt/vol]). Culturable bacteria were identified by 16S rDNA sequence analysis, and their susceptibilities to four biocides and six antibiotics were determined. Microcosms harbored ca. 10 log 10 CFU/g of biofilm, representing at least 27 species, mainly gamma proteobacteria, and maintained dynamic stability. Viable cell counts were largely unaffected by TCSD exposure, but species diversity was decreased, as corroborated by denaturing gradient gel electrophoresis analysis. TCS susceptibilities ranged widely within bacterial groups, and TCS-tolerant strains (including aeromonads, pseudomonads, stenotrophomonads, and Alcaligenes spp.) were isolated before and after TCSD exposure. Several TCS-tolerant bacteria related to Achromobacter xylosoxidans became clonally expanded during dosing. TCSD addition did not significantly affect the community profiles of susceptibility to the test biocides or antibiotics. Several microcosm isolates, as well as reference bacteria, caused clearing of particulate TCS in solid media. Incubations of consortia and isolates with particulate TCS in liquid led to putative TCS degradation by the consortia and TCS solubilization by the reference strains. Our results support the view that low-level exposure of environmental microcosms to TCS does not affect antimicrobial susceptibility and that TCS is degradable by common domestic biofilms.

Effects of Quaternary-Ammonium-Based Formulations on Bacterial Community Dynamics and Antimicrobial Susceptibility

“…Domestic drain microcosms. Domestic drain microcosms were established as described previously (27,28). Briefly, drain biofilm (2.5 g) was macerated with a sterile mortar and pestle and diluted 1:10 in sodium phosphate buffer (22.5 ml, 0.1 M, pH 6.5) containing 0.45% (wt/vol) NaCl which had been prereduced (boiled for 5 min and cooled under a constant stream of anaerobic gas [5:95 CO 2 /N 2 ratio]).…”

“…In order to model more accurately the open nature of a domestic sink drain, the fermentor pans were continuously wetted with untreated tap water (1 ml/h). CDFFs enable the continuous culture of biofilms at accurately set depth (26)(27)(28)(29)(30)(31)37). In all cases, the biofilm (Teflon plug) depth was set at 5.0 mm.…”

“…Kitchen sink drain outlets are a site of considerable bacterial colonization in the home (27) and also an environment that is commonly exposed to biocides at sublethal concentrations (28).…”

“…Effects of QAC exposure on biofilm communities were then investigated with a drain biofilm microcosm previously characterized and validated for stability and utility (27). These microcosms have previously been used to model the effects of TCS exposure in the home (28) and of biocide exposure of dental plaque communities (29,30). Differential plate counts and culture-independent methods (denaturing gradient gel electrophoresis [DGGE]), in conjunction with sequencing (31), were used to characterize the developed communities and the effects of QD exposure therein.…”

Retrospective environmental risk assessment of human pharmaceuticals in the Nordic countries 1997-2007

“…The issue seems to be rather complex since some bacteria like Escherichia coli and Staphylococcus aureus may gain a "low-level" resistance to triclosan (Heath et al, 1999, andFan et al, 2002). These speculations on a general development of resistant bacteria strains have not proven to be correct so far however (McBain et al, 2003, and Aiello et al, 2004, Yazdankhah et al, 2006, but have caused triclosan to become a substance of concern and phase-out in the Nordic countries.…”