Abstract
The emergence of bacterial antibiotic resistance might be transmitting from aquaculture environments to humans and animals. For these reasons, many researchers have been investigating the use of antimicrobial safer compounds that have no harmful effects on fish, consumers and ecosystems. The current study was conducted to investigate the antibacterial activities of allicin, one of the major essential oils of garlic, against some fish pathogenic bacteria as well as the toxic effect of allicin on monosex Nile tilapia (Oreochromis niloticus). Allicin 10% v/v solution in dimethyl sulfoxide (DMSO) was used in this study. The bacterial species investigated were Aeromonas hydrophila, Aeromonas caviae, Aeromonas sobria, Aeromonas. veronii, and Streptococcus iniae. The minimum inhibitory concentrations (MICs) of allicin in DMSO against Aeromonas hydrophila was found to be 125 mu g/ml, while ranged between 250-500 mu g/ml for each of A. caviae, A. sobria and A. veronii. Interestingly, the MIC for Streptococcus iniae was 63 mu g/ml. On contrary, allicin showed no bactericidal activity against the investigated bacteria. Allicin had high toxic effect on tilapia fingerlings while adult tilapia could tolerate its toxic effect.