Evaluation of the impact of tromethamine edetate disodium dihydrate on antimicrobial susceptibility of Pseudomonas aeruginosa in biofilm in vitro.

Abstract

BACKGROUND: Biofilm formation by Pseudomonas aeruginosa has been documented in canine otic isolates. An increase in minimal inhibitory concentration (MIC) for specific antibiotics has been noted for biofilm-embedded bacteria. Tromethamine edetate disodium dihydrate buffered to pH 8 with tromethamine hydrochloride and deionized water (Triz-EDTA(&#xae;)) has been documented to potentiate bactericidal activity when used in combination with topical antibiotics, but the impact on biofilm-embedded bacteria is unknown. HYPOTHESIS/OBJECTIVES: The objective of this study was to evaluate the impact of Triz-EDTA(&#xae;) use on in vitro antimicrobial susceptibility of biofilm-embedded P. aeruginosa. METHODS: Biofilm formation was documented using a microtitre plate assay. Broth microdilution was used to assess the MIC of neomycin, polymyxin B, enrofloxacin and gentamicin for the biofilm-embedded bacteria. The microtitre plate assay was again used to assess the MIC of neomycin, polymyxin B, enrofloxacin and gentamicin for biofilm-embedded bacteria with added Triz-EDTA(&#xae;). RESULTS: Thirty-one isolates from dogs with otitis were tested. Addition of Triz-EDTA(&#xae;) significantly reduced MICs for neomycin (P < 0.003) and gentamicin (P < 0.02) but not for polymyxin B (P = 0.3). Enrofloxacin MICs increased in the presence of Triz-EDTA (P < 0.036). CONCLUSIONS AND CLINICAL IMPORTANCE: Triz-EDTA(&#xae;) may be a useful adjunctive treatment for chronic cases of Pseudomonas otitis where biofilms may have developed, if gentamicin or neomycin is to be used as a topical treatment. In vivo study is required to confirm this effect.