Tris–EDTA significantly enhances antibiotic efficacy against multidrug‐resistant Pseudomonas aeruginosa in vitro
Multidrug‐resistant Pseudomonas aeruginosa commonly complicates chronic bacterial otitis in dogs.
The aim of this in vitro study was to determine the effect of ethylenediaminetetraacetic acid–tromethamine (Tris–EDTA) on the minimal bactericidal concentrations (MBCs) and minimal inhibitory concentrations (MICs) of marbofloxacin and gentamicin for multidrug‐resistant P. aeruginosa isolates from cases of canine otitis.
Eleven isolates were identified as multidrug resistant on disc diffusion; 10 were resistant to marbofloxacin and two were resistant to gentamicin. Isolates were incubated for 90 min with each antibiotic alone and in combination with Tris–EDTA at concentrations of 0.075 μg/mL to 5 mg/mL for marbofloxacin, 0.001 μg/mL to 10 mg/mL for gentamicin and 17.8:4.7 to 0.14:0.04 mg/mL for Tris–EDTA. Positive and negative controls were included. Aliquots of each antibiotic and/or Tris–EDTA concentration were subsequently transferred to sheep blood agar to determine the MBCs, and tryptone soy broth was added to the remaining suspensions to determine the MICs.
Tris–EDTA alone was bacteriostatic but not bactericidal at any concentration. The addition of Tris–EDTA significantly reduced the median MBC (from 625 to 468.8 μg/mL; P < 0.001) and MIC (from 29.3 to 2.4 μg/mL; P = 0.008) of marbofloxacin, and the median MBC (from 625 to 39.1 μg/mL) and MIC (from 19.5 to 1.2 μg/mL) of gentamicin (both P < 0.001).
Tris–EDTA significantly reduced the MBCs and MICs of marbofloxacin and gentamicin for multidrug‐resistant P. aeruginosa in vitro. This may be of use to clinicians managing these infections in dogs.
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Document Type: Research Article
Publication date: October 1, 2013