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Applied and Environmental Microbiology, August 2008, p. 4825-4834, Vol. 74, No. 15
0099-2240/08/$08.00+0     doi:10.1128/AEM.00573-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

In Vitro Study of the Effect of Cationic Biocides on Bacterial Population Dynamics and Susceptibility{triangledown}

Louise E. Moore, Ruth G. Ledder, Peter Gilbert, and Andrew J. McBain*

School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Manchester M13 9PT, United Kingdom

Received 10 March 2008/ Accepted 23 May 2008

Cationic biocides (CBs) are widely used in domestic and public hygiene and to control biofouling and microbial contamination in industry. The increased use of biocides has led to concern regarding possible reductions in biocide effectiveness. Domestic drain microcosms were stabilized for 5 months and then exposed to polyhexamethylene biguanide (PHMB) at 0.1, 0.2, and 0.4g liter–1 over 6 months and characterized throughout by differential culture, together with eubacterial-specific PCR-denaturing gradient gel electrophoresis. Additionally, MICs and minimal bactericidal concentrations (MBCs) for bacteria previously isolated from a domestic drain (n = 18) and the human skin (n = 13) were determined before, during, and after escalating, sublethal exposure (14 passages) to two quaternary ammonium compounds (QAC1 and QAC2), the bisbiguanide chlorhexidine (CHX), and PHMB. Exposure of the drain microcosm to PHMB did not decrease the total viable count although significant (P < 0.01) decreases in recovery were observed for the gram-positive cocci with associated clonal expansion of pseudomonads (from ca. 0.1% of the population to ca. 10%). This clonal expansion was also manifested as elevations in bacteria that could grow in the presence of PHMB, CHX, and QAC1. Decreases in susceptibility (greater than twofold) occurred for 10/31 of the test bacteria for QAC1, 14/31 for QAC2, 10/31 for CHX, and 7/31 for PHMB. Exposure of microcosms to PHMB targeted gram-positive species and caused the clonal expansion of pseudomonads. In terms of prolonged-sublethal passage on CBs, exposure to all the biocides tested resulted in susceptibility decreases for a proportion of test bacteria, but refractory clones were not generated.

* Corresponding author. Mailing address: School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, United Kingdom. Phone: 44 161 275 2360. Fax: 44 161 275 2396. E-mail: andrew.mcbain{at}manchester.ac.uk

{triangledown} Published ahead of print on 30 May 2008.

Applied and Environmental Microbiology, August 2008, p. 4825-4834, Vol. 74, No. 15
0099-2240/08/$08.00+0     doi:10.1128/AEM.00573-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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