Exposure of Acinetobacter baylyi ADP1 to the biocide chlorhexidine leads to acquired resistance to the biocide itself and to oxidants

Abstract

Objectives: The aim of this study was to determine the effect of exposure to sublethal concentrations of chlorhexidine on oxidative stress protection by Acinetobacter baylyi ADP1. Methods: ADP1 cultures were exposed to sublethal concentrations of chlorhexidine prior to being challenged with lethal concentrations of chlorhexidine itself and by oxidants. Oxidant-sensitive dyes and a flow cytometer were used to measure the formation of reactive oxygen species. The role of efflux pumps in chlorhexidine resistance was investigated using a specific inhibitor. Results: Exposure of ADP1 to low concentrations of chlorhexidine induced adaptive and cross-protective responses to chlorhexidine and oxidants (H 2 O 2 and a superoxide anion generator), respectively. Chlorhexidine treatment of ADP1 resulted in the formation of H 2 O 2 and superoxide anions that are probably responsible for the cross-protection against oxidants. Conclusions: Exposure of ADP1 to sublethal concentrations of chlorhexidine confers inducible resistance to lethal concentrations of chlorhexidine itself and to oxidants. An important link was demonstrated between exposure to a biocide and the gaining of resistance to both the biocide and oxidative stress. © The Author 2010. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.