Background and purpose: Measurement of DPPH free radical scavenging is a valid, accurate, and easy method with high repeatability in evaluating the in vitro antioxidant activity of plant extracts. A positive correlation is reported between antioxidant activity and antimicrobial activity. The aim of this study was to evaluate the correlation between antioxidant and antimicrobial activity of medicinal plant extracts.

Materials and methods: The extracts were prepared and DPPH was used to determine free radical-scavenging activity. Antimicrobial effects of hydro-ethanol extract on the bacteria was surveyed using diffusion method in a culture medium Mueller-Hinton agar by paper discs (6 mm) based on Bauer and Kirby instructions.

Results: The ability of medicinal plant extracts in scavenging free radicals was found to be higher in the extracts of Myrtus (89.583 µg/mL) and rosemary (80.921 µg/mL). The antioxidant activity of the extracts increased by increase in concentration of the extract. Meanwhile, in low concentrations of the extract (16 and 32 µg/mL) the highest antioxidant activity of the extract was found in Myrtus and then Rosemary, but at high concentrations (64 µg/mL) it was seen in Teucrium polium extract. Rosemary extract was found to be effective against Escherichia coli and Myrtus extract was the most effective on Listeria bacteria, Salmonella typhimurium, and Staphylococcus aureus.

Conclusion: The results showed that plants with high antioxidant properties have high antimicrobial activity too, such as the extract of Myrtus and rosemary that were the most effective extracts on bacteria.