Veterinary session

The inflammation of the external ear canal in dogs is a common disease in the small animal practice. Numerous bacteria and fungi in conjunction with predisposing factors are the underlying cause of this condition, but the Gram-negative rods provoke the greatest challenge, such as the multiresistant Pseudomonas aeruginosa. Protective biofilm is often produced by this pathogen, making it even more resistant to both the immunesystem and the antimicrobial substances. As a result, there is a growing interest in alternative antimicrobial and antibiofilm substances, as they could enhance the penetration of antimicrobial agents into biofilms, consequently they could make the antimicrobials more efficient.

The aim of our study was to find such substant combinations that are currently not in trade and able to provide synergistic antimicrobial and antibiofilm effect on biofilm-producing P. aeruginosa strains. Beside the antibiotic component, three antibiofilm substances were used in the experiments. One of them is a chelating agent, which is able to enhance antibiotic penetration to the Gram-negative bacteria by connecting to their membranes; another substance is a plant essential oil that decreases the bacterial membrane integrity and additionally a cystein derivative potentially disrupting and inhibiting formation of biofilms. On biofilm producing P. aeruginosa strains we performed individual MIC evaluations of the aforenamed substances, followed by the evaluation of combinations of two and three substances and also studied their efficacy of biofilm disruption on P. aeruginosa biofilms with MTS-formazan and crystal violet dyeing.

As a result of our experiments, we found synergic antibacterial effect in case of the essential oil-chelating substance in a 1:2 ratio combination and in case of the antibiotic-chelating agent combination of two, moreover the antibiotic-essential oil-chelating substance combination of three during our in vitro studies. We explored partial synergism on P. aeruginosa strains with the use of essetial oil-chelating 1:1 and 2:1 proportioned solutions. The effect of the plant essential oil was indifferent in combination with the examined antibiotic.

We are planning on testing these combinations in vivo as active agents for ear drops, intramammary products and other topical formulations, assuming that they could be effective in the therapy of Pseudomonas infections.