Abstract
Antimicrobials are widely applied in aquaculture for treatment of infectious diseases in fish. The increased antimicrobial resistance of fish pathogens to conventional antimicrobial treatment highlights the need for research on the antibacterial properties of natural products—in this case, essential oils (EOs). The aim of the present study was to detect the antimicrobial activity of the essential oils on pathogenic microorganisms found in freshwater fish. Freshwater fish isolates of Aerococcus spp., Aeromonas spp., Enterococcus spp., Escherichia spp., Pseudomonas spp., Shewanella spp., Yersinia spp., and Vagococcus spp. were tested for antimicrobial resistance and antimicrobial activity against 14 commercially available essential oils. Antimicrobial resistance was identified in Pseudomonas spp. isolates against cefepime and ciprofloxacin; while all Aeromonas, Enterococcus, and Yersinia isolates were fully susceptible. All tested EOs revealed antimicrobial activity against the tested freshwater fish isolates at different extents. Cinnamomum camphora exhibited strong antimicrobial activity against Aeromonas spp. (3.12 μL/mL), Enterococcus spp. (0.78–1.56 μL/mL), and Pseudomonas spp. with the MIC method. EOs of Gaultheria procumbens and Litsea cubeba showed strong antibacterial activity against Yersinia spp. and Vacococcus spp. (6.25 μL/mL). The study shows the antimicrobial activity of EOs against the most relevant freshwater fish pathogens and indicates the application opportunities in aquaculture.
Highlights
Essential oils are present in different parts of plants and consist of aromatic and volatile compounds
We found α-limonene to be the dominant constituent in essential oils (EOs) of Boswellia carterii L., Canarium luzonicum Miq.(H), Cinnamomum camphora Nees & Eberm, Litsea cubeba Pers., Melaleuca leucadendron L., and Citrus limon (L.) with 19.8%, 39.7%, 25.1%, 14.3%, 6.9%, and 58.9% respectively
We found that α-santalol (59.0%), α-bergamotene (9.68%), and β-santalol (9.02%) were the major compounds in EO of Santalum album L
Summary
Essential oils are present in different parts of plants and consist of aromatic and volatile compounds. The primary role of EOs is the protection of plants against pathogens, which is attributed to the antimicrobial activity that EOs have shown [1]. The effects of EOs are created by their chemical composition, and an amount of a single compound from different plants, sharing different chemotypes affects the chemical composition of EOs [2]. Different features of EOs have been revealed to have antimicrobial properties, which have been intensively investigated to find out their possible applications for replacements of existing antimicrobial treatments. The antibacterial, antiviral, antifungal, and insecticidal properties of EOs have been demonstrated, which allow us to consider EOs as an alternative of the current antimicrobials used for humans and animals [5,6,7]
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