The use of natural compounds can be found in many species of plants, and this holds much antimicrobial potential against fish pathogens in animal husbandry and fish farmers. In the current study, we studied the antimicrobial activity of the ethanolic extract derived from the leaves of F. villosa against the Aeromonas species: A. sobria, A. hydrophila, and A. salmonicida subsp. salmonicida, as well as Serratia liquefaciens, Yersinia ruckeri, Pseudomonas fluorescens, Shewanella putrefaciens to evaluate the possible use of this plant in preventing infections caused by these fish pathogens in aquaculture. The current study was conducted as a part of an ongoing project between five universities undertaken in the frame of a cooperation program aimed at the assessment of medicinal properties of tropical and subtropical plants. The leaves of F. villosa, cultivated under glasshouse conditions, were sampled at M.M. Gryshko National Botanic Garden (NBG), National Academy of Science of Ukraine. The Aeromonas strains used in our studies were Aeromonas hydrophila (K886), Aeromonas sobria (K825) and Aeromonas salmonicida subsp. salmonicida (St30). These microorganisms originated from the bacterial strain collection of the Department of Fish Diseases at the National Veterinary Research Institute in Puławy, Poland, and had been isolated from fish of two farmed freshwater species exhibiting clinical signs of disease: common carp (Cyprinus carpio L.) (K886 and K825) and rainbow trout (Oncorhynchus mykiss Walbaum) (St30). Bacteria Serratia liquefaciens, Yersinia ruckeri, Pseudomonas fluorescens, Shewanella putrefaciens were isolated both from apparently healthy rainbow trout (Oncorhynchus mykiss Walbaum), as well as from individuals exhibiting clinical signs of the diseases, according to the procedure developed at the Department of Fish Disease of the National Veterinary Research Institute in Poland. Antimicrobial susceptibility of the tested strains was performed by the Kirby-Bauer disc diffusion method (1966) according to the recommendations of the Clinical and Laboratory Standards Institute (CLSI, 2014), with our some modifications. Results of the antimicrobial screening revealed, that F. villosa possessed different antibacterial properties against fish pathogens. The ethanolic extract derived from leaves of F. villosa exhibited the maximum antimicrobial activity against Shewanella putrefaciens, Aeromonas sobria, and Pseudomonas fluorescens. The percentage of increase in the diameters of inhibition zones was 122.7% for Shewanella putrefaciens, 54.9% for Aeromonas sobria, and 48.5% for Pseudomonas fluorescens, respectively. F. villosa exhibited mild antibacterial properties against Serratia liquefaciens, Yersinia ruckeri, Aeromonas hydrophila, Aeromonas salmonicida subsp. salmonicida. Thus, the Shewanella putrefaciens strain exhibited the highest sensitivity to the ethanolic extract derived from leaves of F. villosa, while Serratia liquefaciens and Yersinia ruckeri strains were resistant to this extract. These findings demonstrate that plant extracts derived from plants belonging to the Ficus genus are potential sources of botanical drugs for controlling bacterial infection in aquaculture.
