Veterinary session

A high proportion of dogs come to the veterinary practice with ear complaints. One of the most common causes is external ear canal inflammation, which can be caused secondarily by the highly multi-resistant bacterium Pseudomonas aeruginosa, which is difficult to treat due to its resistance mechanisms and biofilm formation. The main objective of our research was to investigate a potential combination of agents for use in veterinary otolaryngology, where the components have potent antibacterial and potential biofilm-disrupting properties and when used in combination, enhance each other's efficacy. As a second-generation fluoroquinolone, marbofloxacin is one of the most effective antibiotics for the control of P. aeruginosa. Geraniol is a monoterpene alcohol with excellent anti-biofilm activity. Ethylenediaminetetraacetic acid (EDTA) can potentiate the action of marbofloxacin as a metal chelator. We investigated the antibacterial and anti-biofilm effects of the three drugs and their two- and three-drug combinations on biofilm-producing control P. aeruginosa strains and P. aeruginosa from canine otitis externa. A serial passaging of the biofilm-producing P. aeruginosa strain ATCC® 27853™ was performed by testing the minimum inhibitory concentration (MIC). We observed whether the combination with anti-biofilm agents inhibited the spread of resistance to marbofloxacin. In addition, we wondered whether the antimicrobial resistance of P. aeruginosa could be related to the efflux pump function of the bacterium. To this end, we tested twenty-two P. aeruginosa clinical isolates and one control strain (ATCC® 27853™) with and without the active substances and their combinations in the presence and absence of an efflux pump inhibitor (EPI), the active substance carbonyl cyanide-3-chlorophenylhydrazine (CCCP). In addition, the biofilm disruption properties of the active substances and their combinations were investigated on the biofilm of P. aeruginosa strain ATCC® 27853™ using crystal violet and MTS-formosan staining procedures. Our research has revealed synergism, partial synergism or indifferent effects between certain combinations of active substances. Our resistance test results with CCCP suggest that the antibacterial resistance is not due to an efflux-pump function of the tested isolates in the presence of the respective agents. From the results of our biofilm disruption experiment, we concluded that the biofilm disruptive effect of the tested agents and their combinations was not significantly greater when used in combination than when used alone with marbofloxacin.