Study on antibacterial activity and the mechanism of santalol against Staphylococcus aureus CS strain

In order to investigate the antibacterial effects and the mechanism of santalol against Staphylococcus aureus（Sa）, in this experiment, Sa CS strain was used as the research object and the minimum inhibitory concentration(MIC₅₀) of santalol against Sa CS strain was determined by double dilution method. The Karber method was used to calculate half of the lethal dose of Sa CS strain to mice. Forty 4-week-old Kunming mice were randomly divided into 4 groups. First, half of the lethal dose of bacteria were used for challenge by nasal inhalation, and each group of mice was injected with 32, 64, 128 μg/mL of santalol 0.2 mL intraperitoneally; mice untreated with santalol were the control. Normal feeding lasted for 4 days, and the survival of mice was observed; at the end of the experiment, all mice were sacrificed, and lung tissue was taken for bacterial counting, and the antibacterial effect of santalol was measured. SDS-PAGE was used to determine the effect of 16, 32, 64, 128 μg/mL santalol on the expression of soluble protein in Sa CS strain, and bacteria without santalol treatment were used as control. The effect of 32 μg/mL santalol on the expression of cell division-related genes and ribosomal constituent protein-related genes in Sa CS strain was detected by real-time PCR, and the bacteria treated without santalol were used as control. The results showed that the MIC₅₀ of santalol for Sa CS strain was 32 μg/mL. All control mice died within 4 d; 5, 7, and 9 mice treated with 32, 64, 128 μg/mL santalol survived, respectively. Santalol-treated mice had significantly or very significantly lower lung bacterial counts than the controlled mice（P＜0.05 or P＜0.01）. Compared with the control group, the expression of soluble protein decreased after 6 h of treatment with 64, 128 μg/mL santalol. Compared with the control group, the relative expression of ftsZ in cell division-related genes in Sa CS strain treated with santalol was significantly reduced（P＜0.01）. The relative expression of genes rpsJ was significantly downregulated（P＜0.05）. The relative expression of rplB gene and rpoE gene was significantly downregulated（P＜0.01）. The relative expression of ribosomal constituent protein-related genes rpsO, rpsA, rpsS and rpsI was significantly upregulated（P＜0.01）. There was no significant difference in the relative expression of rpsC, rpmJ and rplD genes（P＞0.05）. The results indicated that santalol had in vivo and in vitro antibacterial activity against Sa CS strain, and its antibacterial mechanism might be achieved by reducing cell division-related genes of Sa CS strain, disrupting the expression of ribosome genes and affecting protein expression.