Study on the effect of aqueous and ethanolic extracts of Juglans regia plant on Lactococcus garvieae isolated from meat of rainbow trout (Onchorynchus mykiss)

Lactococcus garvieae (L. garvieae) is the causative agent of lactococcosis in fish. These diseases can be transmitted to humans by direct contact or consumption of infected fish meat. In this study, the susceptibility of L. garvieae to the ethanolic and aqueous extracts of Juglans regia (J. regia) was evaluated. Ethanolic and aqueous extract of the J. regia was prepared and successively diluted to obtain minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against L. garvieae bacteria by successive dilution method. Also, the inhibition of bacterial growth was measured, using disk diffusion method. The results showed that the ethanolic extract of J. regia had bactericidal effect in concentrations of 37.5 mg/ml and also the bacteriostatic effect in the concentration of 18.75 mg/ml. However, the aqueous extract of J. regia, at concentrations of 75 mg/ml showed a bacterial effect and in the concentration of 37.5 mg/ml, the bacteriostatic effect was shown against bacterial growth. Considering the proper effect of these extracts on L. garvieae, more extensive studies was needed in clinical conditions in aquaculture farms. After determining the effective concentration, non-toxicity and the mechanism of their effect, extracts can be used in the treatment and prevention of disease.