In Vitro Activity of Farnesol against Malassezia pachydermatis Isolates from Otitis Externa Cases in Dogs

SIMPLE SUMMARY: Despite the discoveries of new therapeutic antimycotics, the development of drug resistance is still the main clinical challenge in the treatment of mycoses. Data on the presence of new phytopreparations, along with the direct fungicidal effects that interfere with the resistance of fungal pathogens located in the biofilm, are of great interest. Our research focused on four investigations: (1) study M. pachydermatis as a biofilm infection; (2) the search for the strongest biofilm producers and the most resistant strains to antimycotics; (3) check if there is a correlation between the resistance of strains to modern antimycotics and the ability to form biofilms; and (4) study of the effect on three of the best biofilm producers under the action of several concentrations of Farnesol. These experiments confirmed related applications of Farnesol and its research progression in antifungal therapy of otitis externa. ABSTRACT: Chronic otitis externa of dogs is a significant problem due to the prevalence and complexity of the treatment of such animals. There is evidence that in 60–80% of cases of infectious diseases microorganisms located in the biofilm phenotype play the main role. Microorganisms in the biofilm phenotype have a number of advantages, the most significant of which is considered to be increased resistance to various external factors. Among them, a special place is occupied by resistance to antibiotics. In recent decades, research has been conducted at an increasing scale on the role of biofilm infections in various pathologies in veterinary medicine. The etiology and therapy of dog otitis externa caused by Malassezia pachydermatis biofilm has not been fully studied. This is why we consider relevant the scientific and practical aspects of research on the etiology and therapy of dog otitis externa from the position of biofilm infection. In this work, it has been statistically proven that there is a relationship between the optical density of Malassezia pachydermatis biofilms and their sensitivity to drugs, and this relationship is statistically significant. In addition, we have demonstrated that Farnesol has a good antibiofilm effect at a concentration of more 1.6 μM/mL (24% OD decrease of biofilm), and its highest antibiofilm effect (71–55%—more than a half) was observed at a concentration of 200–12.5 μM/mL.