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

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.