In vitro combination effects of natural substances and antimicrobials against Edwardsiella tarda and Streptococcus iniae

Abstract

The purpose of this study is to explore the possibility of essential oils and flavonoids improving the performance of antibiotics, proving a higher efficacy in the presence of natural substances against Edwardsiella tarda and Streptococcus iniae. Increased efficacy was observed in several cases: both essential oils and flavonoids increased antibacterial efficacy of oxytetracycline and flumequine against E. tarda by 2-fold; essential oils and flavonoids increased antibacterial efficacy of nalidixic acid against E. tarda by 4-fold; flavonoids increased antibacterial efficacy of josamycin against S. iniae by 4-fold. The results obtained in this study suggest that essential oils and flavonoids might be especially useful in increasing the antimicrobial activity of nalidixic acid and josamycin against E. tarda and S. iniae in fish. Natural compounds examined in this study could also be useful to help decrease the overuse of antibiotics in fish.

Antibacterial Effect of Siegesbeckia pubescens Extract against Fish Pathogenic Streptococcus iniae

“…thymol MIC 256 µg/mL, carvacrol 256 µg/mL, quercetin 128 µg/mL (Bak et al, 2015). • 0 μg/mL, △ 50 μg/mL, □ 100 μg/mL…”