Antibacterial Activity of Wintergreen Oil

Seven microorganisms were used to evaluate the antibacterial activities of some selected wintergreen essential oils: five Gram-positive bacteria, Bacillus cereus (ATCC-14579), Staphylococcus epidermidis (ATCC-12228), Propionibacterium acnes (ATCC-11827), Staphylococcus aureus (ATCC-29213), and Streptococcus pyogenes (ATCC-19615), and two Gram-negative bacteria, Serratia marcescens (ATCC-14756) and Pseudomonas aeruginosa (ATCC-27853), using the microbroth dilution technique. Tryptic soy agar medium was used to culture all tested bacterial strains. A 5000 μg/mL solution of wintergreen essential oil was prepared in dimethyl sulfoxide (DMSO) and twofold dilution in 100 μL of cation-adjusted Mueller Hinton broth (CAMHB) (Sigma-Aldrich, St. Louis, MO, USA) was added to the top well of a 96-well microdilution plate. The prepared stock solution of essential oils was then serially two-fold diluted in fresh CAMHB to obtain final concentrations of 2500, 1250, 625, 312.5, 156.3, 78.1, 39.1, and 19.5 μg/mL. The freshly harvested bacteria with approximately 1.5 × 10⁸ CFU/mL final concentration were added to each well of 96-well microdilution plates and were incubated at 37 °C for 24 h. Gentamicin (Sigma-Aldrich, St. Louis, MO, USA) and DMSO were used as positive and negative controls, respectively [15 (link),19 (link)].