Pseudomonas aeruginosa PAO1 adapted to 2-phenoxyethanol shows cross-resistance to dissimilar biocides and increased susceptibility to antibiotics

The growth adaptability to increasing concentration of the biocide 2-phenoxyethanol (PE) was determined in Pseudomonas aeruginosa PAO1 (P.a.) as part of efforts to understand and control the biocide tolerance and its effect on cross-resistance to other biocides and resistance to antibiotics. After repeated subculturing in media containing increasing sub-minimum-inhibitory PE concentration, P.a. exhibited an adaptive resistance indicated by two-fold increase in MIC at the 10th passage. The resistance was stable and remained after passaging the strain in further 7 successive passages in PE-free growth media. The strain showed cross-resistance towards dissimilar biocides and displayed increased susceptibility to antibiotics, which was not influenced by the presence of the efflux inhibitor ‘carbonyl cyanide m-chlorophenyl hydrazone’. Outer membranes of adapted strain showed altered protein profile when examined by SDS-PAGE.