In-vitro Antibacterial Potentials of Essential oil from Citrus limon against Selected Pathogenic Bacteria Isolated from Cultured Nile Tilapia (Oreochromis niloticus)

Essential oils (EOs) from medicinal plants like lemon (Citrus limon) are considered promising to replace synthetic antibiotics in aquaculture production due to their ability to improve fish health. The aim of the research was to investigate the in vitro antibacterial potentials of varying levels of lemon EO against Streptococcus agalactiae, Escherichia coli, Staphylococcus aureus and Aeromonas hydrophila isolated from Nile Tilapia. This research was conducted at the Microbiology unit., Kenyan Marine and Fisheries Research Institute, Mombasa, Kenya and Environmental Microbiology and Biotechnology Laboratory, Department of Microbiology, University of Ibadan, Ibadan, Nigeria in December 2021. Extraction of EO from lemon peel was performed using steam hydro distillation. The quantitative and qualitative profiling of extracted oil was performed using Gas Chromatography-Mass Spectrometry. The antibacterial potential of lemon EO was tested against some pathogens using the agar well diffusion method while the Minimum Inhibitory Concentrations (MIC) and Minimum Bactericidal Concentration (MBC) were determined by the broth dilution method. The most abundant chemical was D-Limonene (37.56%), 3-Carene (15.88%) and Terpinen-4-ol (93.4%). The lemon EO at 100% and 50% concentration respectively showed the highest antibacterial activity against S. agalactiae (26.00mm and 28.33mm) and E. coli (33.00mm and 30.00 mm); while the least activity was observed against A. hydrophila (8.33mm and 6.67 mm) at P = .05. The MIC and MBC values revealed that 50% lemon EO inhibited bacterial growth for S. agalactiae whereas it was greater than 50% for S. aureus, E. coli and A. hydrophila. Lemon EO has potential antibacterial properties against tested pathogens that affect cultured fish and could be considered a good candidate for further research to develop new antibacterial drugs in aquaculture.