Study of In-Vitro Antimicrobial Effects of Origanum vulgare and Echinacea purpurea Essential Oils on Lactococcus garvieae

There is growing evidence that resistance to antibiotics is increasing, and because of their wide range of negative impacts on the environment and humans, also accumulative effects in fish meat and hazards for humans, there have been numerous studies conducted using medicinal plants as a healthier alternative to antibiotics.

This study examined the antibacterial effect of two native medicinal herbs (oregano and echinacea mixed essential oil) on Lactococcus garvieae compared with some commercial antibiotics used in fish farms.

The antibacterial activities against a fish bacterial pathogen (Lactococcus garvieae) were tested using the disk diffusion method, followed by the determination of minimum inhibitory (MIC) and bactericidal (MBC) concentrations via sequential dilution of essential oil by Broth Micro Dilution method.

The results showed antimicrobial activities of mentioned mixed essential oil with MIC ≥ 6.25 μL/mL and MBC ≥ 12.5 μL/mL. Also, the measurements of the diameter of inhibitory zones are consistent with the results of MIC and MBC, indicating the positive effect of this plant mix oil Lactococcus garvieae. However, the Lactococcus garvieae was more sensitive to Enrofloxacin (NFX 5), and Sulfamethoxazole & Trimethoprim (SXT) (P<0.05), but the combination of Oregano and Echinacea essential oils performed better than Florfenicol (FF) despite the weaker effects against mentioned two antibiotics.

The results approved the antibacterial activity of the mixed essential oil of oregano and Echinacea against Lactococcus garvieae on the laboratory scale. Using these compounds as a possible substitute for antibiotic compounds requires more clinical studies.