The effects of triclosan on uropathogen susceptibility to clinically relevant antibiotics

Triclosan is a broad-spectrum antimicrobial agent currently used in numerous products including surgical scrubs and ureteral stents. Unfortunately, studies have shown triclosan resistance among several bacterial species. Our objective was to characterize resistance patterns of common uropathogens to triclosan and determine whether triclosan exposure would alter their susceptibility to common antibiotics. We hypothesized that triclosan exposure induces a metabolic stress rendering some bacterial strains more susceptible to other antibiotics.

Using largely clinical isolates comprising seven uropathogenic species, we conducted 24 hour growth experiments to determine triclosan minimal inhibitory concentrations (MIC) for each strain. Based upon these MICs, triclosan was added to agar plates at escalating sublethal concentrations and antibiotic disk diffusion assays were conducted using a range of clinically-relevant antibiotics.

Varying susceptibility patterns were observed across all antibiotics studied. Several antibiotics demonstrated increased efficacy in conjunction with triclosan. The combined effect of triclosan with amoxicillin and gentamicin was superior when considering significant increases in susceptibility, with 6 (86%) and 5 (71%) of the 7 bacterial strains displaying enhanced sensitivity, respectively. The antimicrobial effects of nitrofurantoin and the fluoroquinolones were significantly enhanced for 4 (57%), 4 and 3 (42%) of the 7 pathogens, respectively. The two fluoroquinolones were the only antibiotics where susceptibility was negatively impacted (in one strain each) in combination with triclosan.

The synergistic effects of triclosan and several antibiotics are consistent with a triclosan-dependent metabolic strain and/or membrane disruptive effect, and offers important insight into the combined use of antimicrobial compounds in clinical practice.