Pseudomonas aeruginosa cells adapted to benzalkonium chloride show resistance to other membrane-active agents but not to clinically relevant antibiotics

Abstract

Our objective was to determine whether strains of Pseudomonas aeruginosa can adapt to growth in increasing concentrations of the disinfectant benzalkonium chloride (BKC), and whether co-resistance to clinically relevant antimicrobial agents occurs. Attempts were made to determine what phenotypic alterations accompanied resistance and whether these explained the mechanism of resistance. Strains were serially passaged in increasing concentrations of BKC in static nutrient broth cultures. Serotyping and genotyping were used to determine purity of the cultures. Two strains were examined for cross-resistance to other disinfectants and antibiotics by broth dilution MIC determination. Alterations in outer membrane proteins and lipopolysaccharide (LPS) expressed were examined by SDS-PAGE. Cell surface hydrophobicity and charge, uptake of disinfectant and proportion of specific fatty acid content of outer and cytoplasmic membranes were determined. Two P. aeruginosa strains showed a stable increase in resistance to BKC. Co-resistance to other quaternary ammonium compounds was observed in both strains; chloramphenicol and polymyxin B resistance were observed in one and a reduction in resistance to tobramycin observed in the other. However, no increased resistance to other biocides (chlorhexidine, triclosan, thymol) or antibiotics (ceftazidime, imipenem, ciprofloxacin, tobramycin) was detected. Characteristics accompanying resistance included alterations in outer membrane proteins, uptake of BKC, cell surface charge and hydrophobicity, and fatty acid content of the cytoplasmic membrane, although no evidence was found for alterations in LPS. Each of the two strains had different alterations in phenotype, indicating that such adaptation is unique to each strain of P. aeruginosa and does not result from a single mechanism shared by the whole species.

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

“…Biocide resistance in bacteria is known to involve several mechanisms (Loughlin et al 2002;Abdel Malek et al 2002, 2009Russell 2003) thus when a small increase in MIC is observed it indicates the possible disabling of one biocide target (Gilbert and MacBain 2001). Cross-resistance to BIT on the other hand, showed significant (p < 0.05) three-fold increase in the MIC from 32 to 85 g/mL (Table II).…”

“…A possible explanation for increased resistance to PE is the physiological adaptation of the envelope to prevent entry of the biocide. Changes in susceptibility towards biocides have been correlated with OM changes (Loughlin et al 2002;Abdel Malek et al 2002;Winder et al 2000;Brozel and Cloete 1994). It is known that a major mechanism of resistance to biocides is reduced uptake due to impermeability or efflux (Russell 2003).…”

“…is an opportunistic human pathogen characterized by innate resistance to multiple antimicrobials (Hancock 2000;Loughlin et al 2002). Adaptation of P.a.…”

“…Adaptation of P.a. to disinfectants by serial passage in increasing concentration of biocides is well documented (Loughlin et al 2002;Abdel Malek et al 2002;Winder et al 2000). The presence of constitutive and inducible efflux mechanisms removing a huge range of antimicrobials from the cell has been detected in P.a.…”

Comparative Proteomic Analysis of Streptococcus suis Biofi lms and Planktonic Cells That Identifi ed Biofi lm Infection-Related Immunogenic Proteins

“…In fact, other authors [26] reported that organisms isolated from any given niche, medical, environmental, or industrial, have different mechanisms of adhesion and retention, mainly due to changes in their structural components, such as pili, �mbriae, and adhesive surface proteins that have adapted differently over time through selective pressures. Furthermore, exposure to antimicrobials may as well induce changes in cell surface hydrophobicity and surface charge that can alter bacterial adhesion properties [27].…”