Tris-buffered EDTA Treatment of Bacterial Biofilms

Bacterial biofilms can complicate the treatment of infections because bacteria within the biofilm may evade desiccation, host immune response, and antimicrobial therapy. Recently, biofilm production has been documented in canine isolates of Pseudomonas aeruginosa. In this study, 31 canine otic isolates of multidrug-resistant P aeruginosa previously shown to produce a biofilm were tested to determine whether Tris-buffered EDTA had an impact on their antimicrobial susceptibility. The minimum inhibitory concentration (MIC) of neomycin, polymyxin B, enrofloxacin, and gentamicin were determined for biofilm-embedded bacteria with added Tris-buffered EDTA. The MIC of neomycin and gentamicin decreased with the addition of Tris-buffered EDTA, but not for polymyxin B. The MIC of enrofloxacin increased in the presence of Tris-buffered EDTA.

Otic infections caused by P aeruginosa often present a therapeutic challenge because of multidrug resistance. Antimicrobial efficacy is further hindered when the infective strain forms a biofilm that affords a bullet-proof vest for the pathogen. This study confirmed that clinical resistance to aminoglycosides may be overcome for biofilm-embedded P aeruginosa when used in conjunction with Tris-buffered EDTA. However, the increased MIC of enrofloxacin noted for most strains is quite concerning. Currently clinicians have no mechanism by which to detect a biofilm within the ear canal, so it may be best to avoid this combination until in vivo studies can be performed.—Daniel O. Morris, DVM, MPH, DACVD

Evaluation of the impact of tromethamine edetate disodium dihydrate on antimicrobial susceptibility of Pseudomonas aeruginosa in biofilm in vitro. Pye CC, Singh A, Weese JS. VET DERMATOL 25:120-e34, 2014.