The Effect Of Combination Therapy On The Mutant Selection Window (MSW) Of Acinetobacter Baumannii

Objective(1)To establish a method for determination of a single-drug application andcombination application on the MSW.To determine the MSW of the single-drugapplication and combination application of SCF、LEV、MEM.To compare the change in theMSW and select index of combination application and single application.(standard strainsis MPC99/MIC99, the clinical isolates is MPC90/MIC90).To investigate the affect on MSWof combination application of Acinetobacter baumannii in vitro.(2)combined with the dataof pharmacokinetic and pharmacodynamic,to explore whether there is a need forcombination application,if it is need,how to match the pharmacokinetics figure so that theMSW is closed.The expectation is to provide a solution to clinical rational use ofantimicrobial drugs and increase the service life of antimicrobial drugs.Methods(1)MIC、MPC、MIC99、MPC99for standard strains of Acinetobacter baumanniiand(ATCC19606) were determined by the standard two fold agar dilution methods when thethree kinds of drugs are used alone.When to determination the MPC of the three drugs,weenrich the bacterium by broth and sheep blood plate,to make sure that the total number ofbacteria is more than1010CFU on the MH agar plates of antimicrobial agents of everyconcentration containing.Incubating in35℃incubator,the MPC is the lowest drugconcentration of the drug when there is no colony growth after72hours.When thepreliminary results were determined,to linear decrease antibacterial drug concentration of10%base on the preliminary results of MIC and MPC.To determined the MIC99andMPC99of standard strains of Acinetobacter baumanniiand (ATCC19606) by thismethod.Calculating the MSW and select index (MPC99/MIC99) of the3antimicrobial drugswhen they was used single.When combination application,we stabilize an antibacterialdrug concentration for its MIC99, then twice gradient another antibacterial drug concentration for its MIC99，2MIC99，4MIC99，until near the MPC99.Then to measure theMPC and MPC99of the antimicrobial that twice gradient concentration in the samemethod with the single-drug application.To calculation the MSW and select index(MPC99/MIC99) of combination application.To compare the changes between single-drugapplication and combination application.(2)MIC and MPC for36clinical isolates ofAcinetobacter baumannii were determined by the standard two fold agar dilutionmethods,then to determine the MPC after combination application.And computing theMIC90、MPC90、selection index (MPC90/MIC90)and MSW.To compare the changes of eachset of numerical by the paired t-test.Then to analysis the experiment by combiningpharmacokinetic parameters and the result of standard strain ATCC19606.Result(1)The first part:The MPC of SCF for standard strains of Acinetobacter baumanniiATCC19606was32mg.L-1,the MPC99was22.4mg.L-1.After combining with LEV,the MPCreduced to1.8mg.L-1,the MSW reduced from20.6mg.L-1down to0,the MSW completelyclosed,therefore no longer investigated the selection index.The MPC of LEV for standardstrains of Acinetobacter baumannii ATCC19606was4mg.L-1,the MPC99was3.6mg.L-1.Either combining with SCF or MEM， the MPC all reduced to0.8mg.L-1,theMSW reduced from2.8mg.L-1down to0,the MSW completely closed,therefore also nolonger investigated the selection index.The MPC of MEM for standard strains ofAcinetobacter baumannii ATCC19606was4mg.L-1,the MPC99was3.2mg.L-1.Aftercombining with LEV,the MPC reduced to0.8mg.L-1,the MSW reduced from2.4mg.L-1down to0,the MSW completely closed,therefore also no longer investigated the selectionindex（.2）The second part：The MPC range of SCF for36clinical isolates of Acinetobacterbaumannii was8-32mg.L-1,MPC90was16mg.L-1.After combining with LEV,the MPCreduced to4mg.L-1,the MSW reduced from12mg.L-1down to0,the MSW completelyclosed,therefore no longer investigated the selection index.The MPC range of LEV for36clinical isolates of Acinetobacter baumannii was0.5-2mg.L-1,MPC90was2mg.L-1.Eithercombining with SCF or MEM,the MPC reduced to0.5mg.L-1,the MSW reduced from1.5mg.L-1down to0,the MSW completely closed,therefore also no longer investigated theselection index.The MPC range of MEM for36clinical isolates of Acinetobacterbaumannii was1-2mg.L-1,MPC90was2mg.L-1.After combining with LEV,the MPCreduced to0.5mg.L-1,the MSW reduced from1.5mg.L-1down to0,the MSW completelyclosed,therefore also no longer investigated the selection index.Because the MSW of three drugs that after combination therapy for36clinical isolates of Acinetobacter baumannii all reduced to0,the MSW completely closed.so nolonger use the paired t-test to compare whether there were significant differences in theMPC and MSW after combination therapy.Conclusion(1)The result of standard strains of Acinetobacter baumannii (ATCC19606) and36clinical isolates of Acinetobacter baumannii were substantially the same:the MPC andMSW of LEV and MEM were nearly and all lower.The MPC of SCF was larger and theMSW was wider.Quinolones and carbapenems relative to cephalosporin drugs, ability formutant prevention were better.(2)Either combination therapy,the MPC will reduce and theMSW will completely closed.Combination coarctation even close the MSW ofAcinetobacter baumannii,thereby reduce or even eliminate that the drug-resistant mutantstrains were enrichment and amplification alternative.Therefore, when we use theantimicrobial agents,we can choose a single drug application if the concentration ofantibacterial drugs not fall into the MSW most of the time during treatment;we can choosea combination of antimicrobial drugs for the poor ability of the mutant prevention.