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.

Antimicrobial susceptibility changes and T-OMP shifts in pyrithione-passaged planktonic cultures of Pseudomonas aeruginosa PAO1.

AIMS: The aim of this study was to determine whether passaging Pseudomonas aeruginosa PAO1 with sub-MICs of the pyrithione biocides results in both the induction of decreased susceptibility towards these antimicrobials and associated outer membrane profile changes. METHODS AND RESULTS: Previous work by this group has shown that it is possible to induce susceptibility changes towards the isothiazolone biocides in Ps. aeruginosa PAO1 by successive passages in the presence of increasing sub-MICs of biocide. This procedure was accompanied by the loss of a 35 kDa outer membrane protein, T-OMP. In this experiment, this process was repeated with the biocides sodium pyrithione (NaPT), zinc pyrithione (ZnPT) and cetrimide. The pattern of susceptibility was similar to that observed with the isothiazolone biocides. Upon removal of biocide, the observed MIC did not return to the original pre-exposure value. The onset and development of resistance was accompanied by the loss of T-OMP from outer membrane profiles, which suggests that this is a non-specific membrane channel whose production within the cell is sensitive to biocide presence. The T-OMP reappeared when the cells were passaged in the absence of pyrithione. Cross-resistance studies indicated that induced resistance to one biocide yields partial resistance towards other members of the group and the positive control. CONCLUSIONS: These results indicate that the pyrithione biocides have similar susceptibility profiles in Ps. aeruginosa to those exhibited by the isothiazolones, but that the acquired changes in susceptibility to the pyrithiones is largely irreversible. SIGNIFICANCE AND IMPACT OF THE STUDY: This study indicates that acquired susceptibility changes towards sub-MICs of selected biocides are multifactorial in nature.

Outer membrane protein shifts in biocide-resistant Pseudomonas aeruginosa PAO1.

Benzisothiazolone (BIT), N-methylisothiazolone (MIT) and 5-chloro-N-methylisothiazolone (CMIT) are highly effective biocidal agents and are used as preservatives in a variety of cosmetic preparations. The isothiazolones have proven efficacy against many fungal and bacterial species including Pseudomonas aeruginosa. However, some species are beginning to exhibit resistance towards this group of compounds after extended exposure. This experiment induced resistance in cultures of Ps. aeruginosa exposed to incrementally increasing sub-minimum inhibitory concentrations (MICs) of the isothiazolones in their pure chemical forms. The induced resistance was observed as a gradual increase in MIC with each new passage. The MICs for all three test isothiazolones 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 outer membrane protein, designated the T-OMP, in SDS-PAGE preparations. T-OMP was observed to disappear from the biocide-exposed preparations and reappear when the resistance-induced cultures were passaged in the absence of biocide. 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 resistance towards one biocide resulted in the development of cross-resistance towards other members of the group and the control, thiomersal. It has been suggested that the disappearance of T-OMP from these preparations is associated with the onset of resistance to the isothiazolones in their Kathon form (CMIT and MIT).

Selective cytotoxicity of ricin A chain immunotoxins towards murine cytomegalovirus-infected cells.

Immunotoxins were constructed by linking immunoglobulins specific for murine cytomegalovirus (MCMV) to deglycosylated ricin A chain. Toxicities toward MCMV-infected and uninfected cells were determined by measuring the inhibition of protein synthesis following a 48-h exposure to immunotoxins commencing 24 h after infection. The 50% inhibitory concentrations ranged from 0.4 to 4 micrograms/ml for infected cells and from 22 to 120 micrograms/ml for uninfected cells. Selectivity indices ranged from 30 to 157. Control immunotoxins, which were constructed identically except that the immunoglobulin moiety had no specificity toward MCMV antigens, had 50% inhibitory concentrations of 50 and 100 micrograms/ml toward infected and uninfected cells, respectively.

Selective cytotoxicity towards cytomegalovirus-infected cells by immunotoxins consisting of gelonin linked to anti-cytomegalovirus antibody.

An immunotoxin specific for cells infected with human cytomegalovirus (HCMV) was constructed by attaching the ribosome-inactivating enzyme, gelonin, through a disulfide linkage to polyclonal human immunoglobulin (IgG). In uninfected cells, there was no difference between [35S]methionine incorporation in untreated cultures and those treated with immunotoxin at 100 micrograms/ml. In HCMV-infected cells, there was a significant decrease in [35S]methionine incorporation in the immunotoxin-treated cultures, suggesting a selective cytotoxic effect on the virus-infected cells. An immunotoxin specific for murine cytomegalovirus (MCMV) was prepared by linking gelonin to polyclonal anti-MCMV IgG. Using this same parameter for assay of cytotoxicity, the anti-MCMV immunotoxin had a 50% cytotoxic concentration of 35 micrograms/ml in MCMV-infected cells and greater than 200 micrograms/ml in uninfected cells. MCMV yields measured at 7 days postinoculation were reduced by 2 log10 in cultures treated with immunotoxin at 20 micrograms/ml at 1 day postinoculation. These data suggest immunotoxins may have potential for eliminating CMV-infected cells from the host.