Outer membrane protein shifts in biocide-resistant Pseudomonas aeruginosa PAO1

Benzisothiazolone (BIT), N-methylisothiazolone (MIT) and 5-chloro-N-methyli sothiazolone (CMIT) are highly effective biocidal agents and are used as pr eservatives in a variety of cosmetic preparations. The isothiazolones have proven efficacy against many fungal and bacterial species including Pseudom onas aeruginosa. However, some species are beginning to exhibit resistance towards this group of compounds after extended exposure. This experiment in duced resistance in cultures of Ps. aeruginosa exposed to incrementally inc reasing sub-minimum inhibitory concentrations (MICs) of the isothiazolones in their pure chemical forms. The induced resistance was observed as a grad ual increase in MIC with each new passage. The MICs for all three test isot hiazolones and a thiol-interactive control compound (thiomersal) increased by approximately twofold during the course of the experiment. The onset of resistance was also observed by reference to the altered presence of an out er membrane protein, designated the T-OMP, in SDS-PAGE preparations. T-OMP was observed to disappear from the biocide-exposed preparations and reappea r when the resistance-induced cultures were passaged in the absence of bioc ide. This reappearance of T-OMP was not accompanied by a complete reversal of induced resistance, but by a small decrease in MIC. The induction of res istance towards one biocide resulted in the development of cross-resistance towards other members of the group and the control, thiomersal. It has bee n suggested that the disappearance of T-OMP from these preparations is asso ciated with the onset of resistance to the isothiazolones in their Kathon(T M) form (CMIT and MIT).