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Applied and Environmental Microbiology, June 2008, p. 3541-3550, Vol. 74, No. 11
0099-2240/08/$08.00+0     doi:10.1128/AEM.02879-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Community-Level Assessment of the Effects of the Broad-Spectrum Antimicrobial Chlorhexidine on the Outcome of River Microbial Biofilm Development{triangledown}

J. R. Lawrence,1* B. Zhu,1 G. D. W. Swerhone,1 E. Topp,2 J. Roy,1 L. I. Wassenaar,1 T. Rema,3 and D. R. Korber3

Environment Canada, Saskatoon, Saskatchewan, Canada,1 Agriculture and Agri-Food Canada, London, Ontario, Canada,2 University of Saskatchewan, Saskatoon, Saskatchewan, Canada3

Received 20 December 2007/ Accepted 24 March 2008

Chlorhexidine is a common-use antibacterial agent found in a range of personal-care products. We used rotating annular reactors to cultivate river biofilms under the influence of chlorhexidine or its molar equivalent in nutrients. Studies of the degradation of [14C]chlorhexidine demonstrated that no mineralization of the compound occurred. During studies with 100 µg liter–1 chlorhexidine, significant changes were observed in the protozoan and micrometazoan populations, the algal and cyanobacterial biomass, the bacterial biomass, and carbon utilization. Denaturing gradient gel electrophoresis (DGGE) in combination with statistical analyses showed that the communities developing under control and 100 µg liter–1 chlorhexidine were significantly different. At 10 µg liter–1 chlorhexidine, there was significantly increased algal and cyanobacterial biomass while the bacterial biomass was not significantly affected (P < 0.05). No significant effects on protozoan or metazoan grazing were detected at the 10-µg liter–1 chlorhexidine level. Fluorescent in situ hybridization indicated a significant reduction in the abundance of betaproteobacteria and gammaproteobacteria (P < 0.05). Archaeal cell counts were significantly reduced by both chlorhexidine and nutrient treatments. DGGE and statistical analyses indicated that 10 µg liter–1 chlorhexidine and molar equivalent nutrient treatments were significantly different from control communities. In contrast to community level observations, toxicological testing with a panel of cyanobacteria, algae, and protozoa indicated no detectable effects at 10, 50, and 100 µg liter–1 chlorhexidine. Thus, community level assessment indicated a risk of low levels of chlorhexidine in aquatic habitats while conventional approaches did not.

* Corresponding author. Mailing address: Environment Canada, 11 Innovation Blvd., Saskatoon, Saskatchewan, Canada S7N 3H5. Phone: (306) 975-5789. Fax: (306) 975-5143. E-mail: John.Lawrence{at}ec.gc.ca

{triangledown} Published ahead of print on 31 March 2008.

Applied and Environmental Microbiology, June 2008, p. 3541-3550, Vol. 74, No. 11
0099-2240/08/$08.00+0     doi:10.1128/AEM.02879-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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