Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 5 2 2013 06 15 147 152 EN Lee Seong Wei Faculty of Agro Based Industry, University of Malaysia, Kelantan Jeli Campus, 17600 Jeli, Kelantan, Malaysia. Wendy Wee Department of Fisheries Science, Faculty of Fisheries and Aqua-Industry, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia. 2015 10 16 Background and Objectives: This paper describes chemical composition and antimicrobial activity of Cymbopogon nardus citronella essential oil against Edwardsiella spp. (n = 21), Vibrio spp. (n = 6), Aeromonas spp. (n = 2), Escherichia coli (n = 2), Salmonella spp. (n = 2), Flavobacterium spp. (n = 1), Pseudomonas spp. (n = 1) and Streptococcus spp. (n = 1) isolated from internal organs of aquatic animals. Due to the ban of antibiotics for aquaculture use, this study was carried out to evaluate the potential of citronella essential oil as alternative to commercial antibiotic use against systemic bacteria in cultured aquatic animals. Materials and Methods: The essential oil of C. nardus was prepared by using the steam distillation method and the chemical composition of the essential oil was analyzed by gas chromatography–mass spectroscopy (GC–MS). Minimum inhibitory concentration (MIC) of the essential oil tested against bacterial isolates from various aquatic animals and ATCC type strains were determined using two-fold broth micro dilution method with kanamycin and eugenol as positive controls. Results: A total of 22 chemical compounds were detected in C. nardus essential oil with 6-octenal, 3, 7-dimethyl- or citronellal representing the major compounds (29.6%). The MIC values of the citronella oil ranged from 0.244 µg/ml to 0.977 µg/ml when tested against the bacterial isolates. Conclusion: The results of the present study revealed the potential of C. nardus essential oil as alternative to commercial antibiotics for aquaculture use. https://ijm.tums.ac.ir/index.php/ijm/article/view/614 https://ijm.tums.ac.ir/index.php/ijm/article/download/614/387