Chemical composition and antimicrobial activity of the essential oil of Syzygium aromaticum flower bud (Clove) against fish systemic bacteria isolated from aquaculture sites

This paper describes the chemical composition and antimicrobial activity of the essential oil of Syzygium aromaticum against Vibrio spp. (n = 6), Edwardsiella spp. (n = 21), Aeromonas spp. (n = 2), Escherichia coli (n = 2), Flavobacterium spp. (n = 1), Salmonella spp. (n = 2), Streptococcus spp. (n = 1) and Pseudomonas spp. (n = 1) isolated from aquaculture sites as well as seven reference strains of bacteria, namely, Escherichia coli (ATCC 25922), Citrobacter freundii (ATCC 8090), Aeromonas hydrophila (ATCC 49140), Pseudomonas aeruginosa (ATCC 35032), Streptococcus agalactiae (ATCC13813), Edwardsiella tarda (ATCC 15947) and Yersinia enterocolitica (ATCC 23715). Nowadays, most antibiotics are no longer effective in controlling diseases in aquaculture, especially fish systemic bacterial diseases, due to increasing incidences of antibiotic resistance among pathogenic bacteria. Furthermore, many countries have banned antibiotics in aquaculture use due to public health concerns and environmental hazards. Therefore, this study was carried out to evaluate the potential of the essential oil of S. aromaticum as an alternate commercial antibiotic to antimicrobial agents against fish systemic bacteria in aquaculture. The essential oil of S. aromaticum was prepared using a steam distillation method, and the chemical composition was analysed using Gas chromatography-mass spectroscopy (GC-MS). Minimum inhibitory concentration (MIC) values of the essential oils against the tested bacteria were determined using the broth two fold micro dilution method, with kanamycin and eugenol as positive controls. The MIC values of the essential oil of S. aromaticum ranged from 0.015 μg·mL⁻¹ to 0.062 μg·mL⁻¹ against the tested bacterial isolates. A total of nine chemical compounds were detected in the essential oil, with eugenol (49.0%) and caryophyllene (7.5%) being the major compounds. The results of the present study indicate that the essential oil of S. aromaticum shows a huge potential to substitute commercial antibiotics as antimicrobial agents for aquaculture use.