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The diversity of culturable bacteria inhabiting the Baltic Sea surface waters was more divergent at a polluted location than at clean areas. The most important members of the family Enterobacteriaceae that are pathogenic to fish are the enteric redmouth disease agent, Yersinia ruckeri and two species of Edwardsiella, E. tarda and E. ictaluri, Serratia, Proteus and Citrobacter have all been implicated as potential fish pathogens. The use of pharmaceutical substances is rather limited in fish compared to mammalian therapeutics. Medicinal herbs play an alternative role to antibiotic therapy in aquaculture. Ficus species (Moraceae) leaves possess great medicinal potential for the therapy of bacterial and fungal infections and may be used as a natural antiseptic and antimicrobial agent in veterinary. Accordingly, these products can be used in aquaculture as therapeutic and prophylactic agents against fish pathogens, with antimicrobial properties. Present study aimed to investigate the in vitro antimicrobial activity of the ethanolic leaf extracts of various Ficus species against fish pathogen, Citrobacter freundii. The antimicrobial susceptibility testing was done on Muller-Hinton agar by disc diffusion method (Kirby-Bauer disk diffusion susceptibility test protocol). Our results demonstrate that various species of Ficus had mild antibacterial in vitro activity against C. freundii isolated locally from infected eel (Anguilla anguilla L.). The results proved that the extracts from F. drupacea, F. septica, F. deltoidea as well as F. hispida, F. mucuso, F. pumila, F. craterostoma exhibit a favorable antibacterial activity against C. freundii. These validate scientifically their inhibitory capacity attributed by their common use in folk medicine and contribute towards the development of new treatment options in aquaculture based on natural products. The chemical analysis of the aforementioned plant extracts should be performed to determinate their chemical composition and identify the exact phytocompounds responsible for antimicrobial activity against C. freundii. In addition, they should be subjected to pharmacological evaluations with the aim of assessing their in vivo efficacy, toxicity, potential adverse effects, interactions and contraindications. Given the increasing rate of resistance development in bacterial pathogens in aquaculture environments, medicinal plants with antibacterial properties are very important as natural resources for new active compounds.
Key words: antibacterial activity, Citrobacter freundii, infected eel (Anguilla anguilla), Ficus spp., ethanolic extracts, zone of growth inhibition