Relationship between susceptivity to triclosan sensitization by outer membrane permeabilization and cell surface hydrophobicity properties in opportunistically pathogenic Serratia species

BACKGROUND: The nosocomial opportunists Pseudomonas aeruginosa and Serratia marcescens are atypically resistant to the hydrophobic biocide triclosan due largely to outer membrane impermeability properties for hydrophobic substances. However, we have recently shown that the degree of cell envelope impermeability for triclosan differs dramatically among other opportunistically pathogenic Serratia species. Moreover, susceptivity to sensitization to triclosan by outer membrane premeabilization also differs among other intrinsically resistant species. The purpose of the present study was to determine if cell surface hydrophobicity (CSH) properties underlie susceptivity to triclosan sensitization by outer membrane premeabilization in selected species as we further characterize their cell surface properties in anticipation of investigating their propensities to form in vitro biofilms.METHODS: Three Serratia species (marcescens, fonticola, and odorifera) exhibiting disparate degrees of susceptivity to triclosan sensitization by outer membrane premeabilization were examined to determine their susceptibility levels to mechanistically-disparate hydrophobic molecules and their CSH properties. Intrinsic resistance to hydrophobic antibacterial agents was assessed using a standardized disk agar diffusion bioassay. CSH was determined using conventional crystal violet binding, hydrocarbon adherence, and 1-N-phenylnapthylamine uptake assays routinely employed in this laboratory.RESULTS: S. marcescens and S. fonticola were intrinsically resistant to all mechanistically-disparate hydrophobic antibacterial agents examined to include triclosan, while S. odorifera was susceptible. The CSH properties of all these differed only slightly, despite the disparate susceptivities of the two triclosan-resistant species to triclosan sensitization.CONCLUSION: These data suggest that phenotypic differences seen in three opportunistic Serratia species with regard to intrinsic resistance to hydrophobic antibacterial agents in general, and triclosan specifically are at least due in part to disparate abilities of their outer membranes to exclude hydrophobic substances. Moreover, susceptivity to triclosan sensitization by outer membrane premeabilization in the triclosan-resistant species S. marcescens and S. fonticola appears not to be influenced by differences in cell surface hydrophobicity properties

Influence of cell surface hydrophobicity properties on susceptivity to triclosan sensitization by outer membrane permeabilization in opportunistically pathogenic Serratia species

Unlike most hydrophobic molecules, the biocide triclosan is able to penetrate the gram-negative bacterial outer membrane. The nosocomial opportunists Pseudomonas aeruginosa and Serratia marcesens are typically resistant to triclosan due largely to outer membrane impermeability properties for hydrophobic substances. However, we have recently shown that the degree of outer membrane involvement differs among disparate opportunistically pathogenic Serratia species. Cell surface hydrophobicity (CSH) properties underlie susceptivity to triclosan sensitization by outer membrane permeabilization in opportunistic Serratia species. A model system consisting of opportunistic Serratia species (marcesens, fonticola, and odorifera) exhibiting disparate degrees of susceptivity to hydrophobic antibacterial agents and triclosan sensitization by outer membrane permeabilizer compound 48/80 were examined. Overall susceptability to disparate hydrophobic antibacterial agents was determined using conventional disc agar diffusion and macrobroth dilution bioassays. Batch culture kinetics with triclosan and outer membrane permeabilizer compound 48/80 allowed analysis of cell envelope involvement in intrinsic triclosan resistance. CSH was determined using the hydrocarbon adherence method. S. marcesens and S. fonticola intrinsically resistant to hydrophobic antibacterial agents including triclosan, while S. odorifera was susceptible. CSH properties differed only slightly compared with control organisms, regardless of how susceptive they were to triclosan sensitization. These data suggest that the phenotypic differences seen in three opportunistic Serratia species with regard to intrinsic resistance to triclosan are at least partly due to disparate outer membrane exclusion potential. Moreover, susceptivity to triclosan sensitization by outer membrane permeabilization appears not to be influenced by CSH properties

Influence of outer membrane permeabilization on intrinsic resistance to the hydrophobic biocide triclosan in opportunistic Serratia species

Triclosan is a hydrophobic antimicrobial agent commonly employed in health care settings. While it exhibits broad-spectrum antibacterial properties, the gram-negative nosocomial opportunists Pseudomonas aeruginosa and Serratia marcescens are atypically refractory. Intrinsic resistance to triclosan in P. aeruginosa is largely due to its outer membrane impermeability properties for hydrophobic and bulky substances. The present study was undertaken to determine the relationship between triclosan and the outer cell envelopes of thirteen strains of ten Serratia species reported to be opportunistic pathogens in humans. General intrinsic resistance to hydrophobic and other outer membrane impermeant compounds was assessed using cultural selection, disk agar diffusion, and macrobroth dilution bioassays. Uptake of the hydrophobic fluorescent probe 1-N-phenylnapthylamine was assessed in four disparate strains of S. marcescens. Batch culture kinetics in the presence of combinations of triclosan and outer membrane permeabilizer compound 48/80 allowed analysis of outer membrane involvement in intrinsic resistance. Aggregate results revealed that individual species ranged in response to hydrophobic and bulky molecules from generally refractory to extremely susceptible. Moreover, susceptivity to triclosan sensitization by chemical disruption of outer membrane exclusionary properties differed markedly among species which exhibited intrinsic resistance to triclosan. These data suggest that disparate opportunistic pathogens within the genus Serratia differ phenotypically regarding the degree to which outer membrane exclusion contributes to intrinsic resistance for impermeant molecules in general, and triclosan specifically. Ancillary resistance mechanisms appear to contribute in some species and may involve constitutive multi-drug efflux systems.ImportanceA paucity of knowledge exists regarding the cellular and molecular mechanisms by which opportunistically pathogenic members of the genus Serratia are able to infect immunocompromised and otherwise susceptible individuals, and then evade chemotherapy. This is especially true for species other than Serratia marcescens and Serratia liquefaciens, although much remains to be learned with regard to the nature of key virulence factors and infection mechanisms which allow for the typically nosocomial acquisition of even these species. The research described in the present study will provide a better understanding of the contribution of outer cell envelope permeability properties to the pathogenicity of these opportunistic species in an ever-increasing susceptible patient population. It is our hope that greater knowledge of the basic biology of these organisms will contribute to the mitigation of suffering they cause in patients with underlying diseases