Disparate outer membrane exclusionary properties underlie intrinsic resistance to hydrophobic substances in Pseudomonas spp. isolated from surface waters under triclosan selection

Abstract

Representative members of surface water microbiota were obtained from three unrelated municipal sites in Oklahoma by direct plating under selection by the hydrophobic biocide triclosan. Multiple methods were employed to determine if intrinsic triclosan resistance reflected resistance to hydrophobic molecules by virtue of outer membrane impermeability. While all but one organism isolated in the absence of triclosan were able to initiate growth on MacConkey agar, only one was able to initiate significant growth with triclosan present. In contrast, all bacteria selected with triclosan were identified as Pseudomonas spp. using 16S RNA gene sequencing and exhibited growth comparable to Pseudomonas aeruginosa controls in the presence of hydrophobic antibacterial agents to include triclosan. Two representative bacteria isolated in the absence of triclosan allowed for greater outer membrane association with the fluorescent hydrophobic probe 1-N-phenylnapthylamine than did two triclosan-resistant isolates. Compound 48/80 disruption of outer membrane impermeability properties for hydrophobic substances either partially or fully sensitized nine of twelve intrinsically resistant isolates to triclosan. These data suggest that outer membrane exclusion underlies intrinsic resistance to triclosan in some, but not all Pseudomonas spp. isolated by selection from municipal surface waters and implicates the involvement of concomitant triclosan resistance mechanisms.

Keywords:

• Surface water
• triclosan
• Pseudomonas aeruginosa
• Pseudomonas fluorescens
• outer membrane
• intrinsic resistance
• hydrophobic biocides
• novobiocin
• Acidovorax
• Pararheinheimera
• Rheinheimera

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

We are grateful to the National Institute of General Medical Sciences of the National Institutes of Health [Grant No. 8P20GM103447] for two IDeA Networks of Biomedical Research Excellence (INBRE) awards to M.C. and A.W., Oklahoma State University Center for Health Sciences Intramural Grant Program for funding, and Dr. S.A. Ruskoski for assisting with obtaining isolates from surface water sites.