Background: The essential oil of Satureja khuzistanica exhibits broad-spectrum antimicrobial activity. The major component of S. khuzistanica essential oil (EO) is shown to be carvacrol. We studied the mechanism of S. khuzistanica EO action on Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923.
Methods: Susceptibility of the two organisms to S. khuzistanica EO was measured by disc diffusion. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were also determined using broth micro dilution. To determine the mechanism of S. khuzistanica EO, overnight cultures of bacteria were subjected to MIC concentrations of EO for 1 h, External EO was removed by centrifugation at 8000 rpm and the cells were lysed, centrifuged and the supernatants were used to measure the internal EO concentration at OD range of 250-300 nm. The potassium ion concentrations of both bacteria were measured before and after exposure of the cell suspension to 1/2 MIC of the EO for 0, 30 and 60 minute by atomic absorption.
Results: The Disc test results showed marked susceptibility to the EO with inhibition zones of 26 mm for E. coli and 31 mm for S. aureus, MIC and MBC values confirmed the disc test results and were 0.62 mg/ml (0.08% v/v) for both isolates. UV spectrometry showed the presence of EO in the supernatants of EO treated E. coli and S. aureus, suggesting increased permeability of cell membranes. S. khuzistanica EO also induced leakage of potassium ions from E. coli and S. aureus cells at 1/2 MIC concentrations.
Conclusion: Inhibitory and sub-inhibitory concentrations of Satureja khuzistanica EO can affect membrane permeability and possible damage to the bacterial cytoplasmic membrane.