Abstract: In order to study their antimicrobial effects, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 10 plant essential oils against Staphylococcus saprophyticus were determined by the bacteriostatic circle and broth dilution methods. The most effective one was selected to further investigate its antimicrobial mechanism. The results showed that cinnamon essential oil had the best bacteriostatic effect on Staphylococcus saprophyticus. The diameter of the inhibition zone was (24.10 ± 2.55) mm, and both MIC and MBC were 1 mg/mL. After being treated with cinnamon essential oil at MIC and 2 MIC, the growth of Staphylococcus saprophyticus was completely inhibited at 5 h. Cinnamon essential oil could destroy the cell membrane integrity of Staphylococcus saprophyticus, leading to an increase in the activity of extracellular alkaline phosphatase (AKP) and the leakage of intracellular protein, and affect the integrity and metabolism system of the cell wall and cell membrane, and this effect was positively related to its concentration. After being treated with cinnamon essential oil, the cell surface of Staphylococcus saprophyticus became obviously shrunk and no longer dense, and bacterial dissolution and cohesion appeared. Moreover, some bacterial cells were disrupted, leading to the leakage of intracellular contents, causing the outer membrane to fall off, and finally leading to bacterial death. In conclusion, cinnamon essential oil has a significant effect on Staphylococcus saprophyticus. It exerts its bacteriostatic effect by destroying the cell wall and cell membrane, and inhibiting the formation of biofilm.

Key words: plant essential oil; cinnamon essential oil; Staphylococcus saprophyticus; antimicrobial mechanism; biofilm