BACKGROUND: 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.OBJECTIVES: 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.METHODS: 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.RESULTS: 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 &amp; 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.CONCLUSIONS: 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.

In the present study, ten herbal extracts, Citirus unchiu Markovich, root and stem of Berberis koreana, Morus alba, Dendrobium moniliforme, Aster gramineus, A. scabar, Alisma canaliculatum, Fallopia japonica and Origamum (O.) vulgare were determined to examine anti-mycoplasmal activity. Among them, O. vulgare extract (OVE) showed strong anti-mycoplasmal activity and was analyzed by gas-chromatography/mass spectrometry (GC/MS). As the results, OVE was consisted of carvacrol (68.78%), o-cymene (9.80%), terpinene (7.61%) and thymol (4.03%) as main ingredients. To investigate inflammatory activity by intact pathogenic Mycoplasma hyoneumoniae (M. hyo) at 30 ㎍/mL, we examined induced transcription of proinflammatory cytokines such as cyclooxygenase-2, tumor necrosis factor-a, interleukin (IL)-1, IL-6 and inducible nitric oxide synthase in RAW 264.7 cells. With the above results, we further investigated whether OVE could reduce inflammation induced by M. hyo at minimal inhibitory concentration. The result showed that 32 ㎍/mL of OVE inhibited nitric oxide production by 60%. This study also evaluated the combination of OVE with antibacterials against M. hyo for application. Based on these results, it could be concluded that M. hyo induces inflammation in RAW 264.7 cells and OVE protects this inflammation, indicating that OVE may be useful for industrial animals.

The aim of this study was to evaluate the antimicrobial activity and determine the minimum bactericidal concentration (MBC) of the essential oils derived from Origanum vulgare (oregano), Melaleuca alternifolia (tea tree), Cinnamomum cassia (cassia), and Thymus vulgaris (white thyme) against Salmonella Typhimurium, Salmonella Enteritidis, Escherichia coli, Staphylococcus aureus and Enterococcus faecalis. The study also investigated the ability of these different bacterial strains to develop adaptation after repetitive exposure to sub-lethal concentrations of these essential oils. The MBC of the essential oils studied was determined by disc diffusion and broth dilution methods. All essential oils showed antimicrobial effect against all bacterial strains. In general, the development of adaptation varied according to the bacterial strain and the essential oil (tea tree > white thyme > oregano). Therefore, it is important to use essential oils at efficient bactericidal doses in animal feed, food, and sanitizers, since bacteria can rapidly develop adaptation when exposed to sub-lethal concentrations of these oils.