Antibacterial In Vitro Properties of Silver Sulfadiazine in Combination with Tris-EDTA and N-Acetylcysteine Against Pseudomonas aeruginosa Isolates from Dogs with Suppurative Otitis

Pseudomonas aeruginosa otitis is common in dogs and antibiotic-resistant strains are often isolated. We are unaware of reports evaluating the combination of silver sulfadiazine (SSD) with a biofilm disruptor solution containing Tris-EDTA (tromethamine-ethylenediaminetetraacetic acid) and N-acetylcysteine (Tris-NAC). Forty-eight P. aeruginosa strains from dogs with suppurative otitis were analysed using the agar well diffusion method. A volume of 70 μL of Tris-NAC, a water solution of 10% SSD and their combination in equal amount was pipetted into the designated wells. After incubation, the diameter of the inhibition zone was measured. A synergy experiment using the checkerboard assay was performed to look at any potential synergistic effects of SSD and Tris-NAC against only 10 randomly selected isolates of P. aeruginosa. The samples tested with Tris-NAC + 10% SSD solution, compared with the samples tested with 10% SSD alone, demonstrated significantly higher inhibition zones against P. aeruginosa, p < 0.00001. The checkerboard assay results showed an additive effect between the two compounds. The use of 10% SSD could be evaluated as a therapeutic tool against strains of P. aeruginosa if combined with Tris-NAC.