Comparison of Antimicrobial Effects of Ethanolic and Methanolic Extracts of Lavender (Lavandula Stoechas L.) with Antibiotics on some Common Nosocomial Bacteria

The use of herbal products with antimicrobial properties has widely been considered by researchers in recent years. Plant extracts such as lavender extract have a specific importance and role in terms of its application in pharmaceutical and medical industries due to its specific phenolic acids and terpenoid compounds. The aim of the present study was to evaluate the antibacterial properties of lavender extracts on some common nosocomial pathogenic bacteria in comparison with antibiotics in vitro.

In the present empirical study, top flowering part of lavender plant was used to prepare the ethanolic and methanolic extracts at different concentrations (500, 250, 125, 62.5, 31.25, 15.62, 7.81 mg/dl) using maceration method. The high performance liquid chromatography (HPLC) apparatus was used to determine the value of phenolic acids including rosmarinic acid and caffeic acid in the obtained extracts. To determine the diameter of growth inhibition zone and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) from agar dilution method and microdilution procedure were used against four strains of common pathogenic bacteria including Salmonella typhimurium, Shigella dysenteriae, Staphylococcus aureus, and Streptococcus pyogenes using well diffusion and microdilution techniques. Data were analyzed using One-way ANOVA in three replications at the probability level of p <0.01.

The amount of both compounds, rosmarinic acid (4.6±0.5 g/100 g DW), and caffeic acid (2.7±0.2 g/100 g DW) were higher in methanolic extract compared with those of ethanolic. Among the different concentrations of lavender ethanolic extract, only 500 and 250 mg/dl of the extract were efficient by creating 12±0.1 and 10±0.2 mm in diameter of growth inhibition zone, respectively. The MBC of all antibiotics and pathogenic bacteria was obtained at a concentration of 125 mg/dl of methanolic extract. However, the MIC for Staphylococcus aureus and Shigella dysenteriae was 250 mg/dl of the extracts.

The methanolic extract of lavender had a better inhibitory effect compared with the ethanolic extract against the tested bacteria mainly due to the higher content of phenolic acids.