Study On In Vitro And In Vivo Effects Of Fusidic Acid Combined With Baicalein On Staphylococcus Aureus And Its Mechanism

Objective:To explore the in vitro and in vivo antibacterial effects of Fusidic acid(FA)combined with baicalein(BE)on Staphylococcus aureus and the effects of Mutant prevention concentration(MPC)and biofilm mechanism.Methods:1.Taking 13 strains of Staphylococcus aureus(SA)as the object of study,based on the single or combined application of fusidic acid and baicalein,microbroth dilution method and microcheckerboard dilution method were adopted.Its Minimum inhibitory concentration(MIC)for SA was monitored separately,and part of inhibitory concentration index(Fractional inhibitory concentration index(FICI)was calculated.To evaluate the combined effect of the two.The time bactericidal curve was used to determine the number of bacterial colonies of fusidic acid and baicalein in 24h after single and combined use,and the time bactericidal curve was drawn.2.MPC and Mutant selective window(MSW)of 5strains of Staphylococcus aureus were tested with double AGAR dilution method to compare the changes of resistant mutation window after fusidic acid alone and combined with baicalein.3.Establishing the mouse pneumonia model with Methicillin resistant Staphylococcus aureus(MRSA)infection in vivo,The changes of vital signs,lung organ index,colony colonization number and serum inflammatory factors in each group of mice were detected after fusidic acid and baicalein alone or combined treatment.4.Staphylococcus aureus biofilm model was established,and the formation ability of colony biofilm was measured by crystal violet staining method,and the inhibitory and destructive effects of fusidic acid combined with baicalein on Staphylococcus aureus biofilm were compared respectively.Results:1.The MIC range of fusidic acid against 13 strains of Staphylococcus aureus was0.25-4μg/m L,and that of baicalein against 13 strains of Staphylococcus aureus was128-256μg/m L.The results of in vitro experiment showed that 53.8%was synergistic,30.8%was additive and 15.4%was unrelated to fusidic acid combined with baicalein on13 strains of golden grape balls.The optimal bacteriostatic concentration of fusidic acid was reduced by 75%and 75%compared with fusidic acid alone against ATCC29213 and ATCC43300,respectively,and the optimal bacteriostatic concentration of baicalein was decreased by 93.75%and 93.75%compared with baicalein alone against ATCC29213 and ATCC43300.Compared with fusidic acid alone,the optimal bacteriostatic concentration of fusidic acid was reduced by 50%-98.4%against 11 clinical strains such as SA51 and MRSA212.Compared with baicalein alone against 11 clinical strains,such as SA51 and MRSA212,the optimal inhibitory concentration of baicalein decreased by 0%to 93.75%.The time bactericidal curves of fusidic acid and baicalein against three strains of Staphylococcus aureus showed that fusidic acid(1/2MIC)combined with baicalein(1/2MIC)had synergistic bactericidal effects on Staphylococcus aureus ATCC29213,ATCC43300 and MRSA210702212 at 24h.The bactericidal effect was more obvious with the increase of fusidic acid concentration(1MIC).2.The MPC_Sof fusidic acid alone were256,256,128,>256 and>256μg/m L for ATCC29213,ATCC43300,MRSA212,MRSA118 and SA51,and the SI values were 512,256,64,>512 and>256,respectively.For ATCC29213,fusidic acid combined with baicalein decreased the MPC of fusidic acid from 256 to 16μg/m L.For ATCC43300,the MPC value of fusidic acid decreased from256 to 16μg/m L.For clinical strain MRSA212,the MPC value of fusidic acid decreased from 128 to 16μg/m L.For clinical strain MRSA118,the MPC value of fusidic acid decreased from>256 to 8μg/m L.For clinical strain SA51,the MPC value of fusidic acid decreased from>256 to 32μg/m L.The SI of the above 5 strains decreased by 16,16,8,32,8 times,respectively.3.The combined group had the least effect on the vital signs of the mice infected with Staphylococcus aureus,and the experimental results of the lung organ index,the number of colonization of staphylococcus aureus in the lung and the inflammatory factors in the serum of the mice showed that the treatment effect of the combined group on the pneumonia of the mice with staphylococcus aureus was significantly better than that of the fusidic acid and baicalein monotherapy groups,with significant statistical difference(P<0.001).4.Both fusidic acid and baicalein alone and in combination showed different degrees of inhibition and destruction on the growth of Staphylococcus aureus biofilm.For Staphylococcus aureus ATCC29213,ATCC43300 and MRSA212,the inhibition rate and destruction rate of Staphylococcus aureus in combination group were higher than those in fusidic acid and baicalein monologic groups.Conclusion:Fusidic acid combined with baicalein has synergistic bactericidal effect on Staphylococcus aureus.The MSW of fusidic acid was relatively wide when it was applied alone.When combined with baicalein,the MSW of fusidic acid was significantly reduced,which slowed down the development of drug resistance of fusidic acid.The combination of fusidic acid and baicalein in the treatment of staphylococcus aureus infection mice was better than fusidic acid and baicalein alone.Fusidic acid and baicalein play a synergistic antibacterial role by inhibiting the growth of Staphylococcus aureus biofilm.