Development of new preparations based on essential oils and polymeric guanidine derivatives for the prevention of bacterial infections and mycotic pathogens in cyprinids

Purpose. To select the optimal composition of a preparation based on essential oils and polymeric guanidine derivatives for the prevention of bacterial infections and mycoses, particularly saprolegniosis in cyprinids. Methodology. The study material included Daphnia magna, and clinically healthy Cyprinus carpio (Linnaeus, 1758). Maximum tolerated concentration (MTC), lethal concentration (CL100), and median lethal concentration (CL50) were determined on these test organisms. Compositions of essential oils with polyhexamethyleneguanidine (PHMG), zinc oxide nanoparticles, and antibiotics were tested. To determine the antibacterial activity of the experimental compositions, strains Aeromonas hydrophila, A. salmonicida, and Pseudomonas fluorescens were used, and to determine the antifungal activity, strains Saprolegnia spp. and S. parasitica were used. Findings. The CL100/24, CL100/48, and MTC values obtained from Daphnia magna and Cyprinus carpio for both individual ingredients and about 50 of their combinations enabled the identification of the most promising formulations. Microbiological tests preliminarily determined the most effective combinations. The best antibacterial properties were demonstrated by combinations of PHMG with thyme, cinnamon, and oregano essential oils, as well as PHMG with colloidal silver (Ag-colloid). Tests on Saprolegnia parasitica and Saprolegnia spp. showed that the most effective combination was PHMG with oregano essential oil. Originality. Toxicity parameters for aquatic organisms were established for compositions based on essential oils, polymeric guanidine derivatives, and zinc oxide nanoparticles, along with their antimicrobial and antifungal properties. The optimal composition, ingredient concentrations, and treatment conditions were determined. Practical Value. The results can serve as a foundation for the development of new environmentally safe antibacterial and antifungal agents for their use in aquaculture. Keywords: essential oils, polyhexamethylene guanidine, aquatic organisms, antimicrobial agents, antifungal agents.