Mutant Prevention Concentration And Resistance Mechanisms Of Moxifloxacin And Cefoperazone/Sulbactam Against Carbapenem-resistant Acinetobacter Baumannii

Objective1. To determine whether there is synergistic when treated with MFX and/orCFS against clinical isolates of CRAB.2. To study the change of mutant prevention concentration in carbapenem-resistant Acinetobacter baumannii (CRAB) treated with moxifloxacin (MFX)and/or cefoperazone/sulbactam (CFS) in vitro.3. To study the resistant mechanism of CRAB when treated with MFX+CFS.Methods1. we determined the minimum inhibitory concentration (MIC) of30clinicalisolates of CRAB treated with MFX and/or CFS by checkerboard microdilutionassay.2. we determined the MPC of30clinical isolates of CRAB treated withMFX and/or CFS by agar plate dilution assay, which inoculated≥1010CFU·mL-1clinical isolates enriched in broth onto a series of drug-containing agar plates;we got the samples at different time and draw the time-killing carves bycounting the colonies.3. PCR and DNA sequence analyses for quinolones(GyrA, ParC) and β-lactamase genes(blaTEM). Results1. MICs range of MFX or CFS aganst30strains of CRAB were0.125~2mg·L-1,8~32mg·L-1, respectively; and MICs decreased significantly afterMFX+CFS, comparing with MFX or CFS; concentration-cumulative inhibitionpercentage curve move to the left; Our study showed that there issynergistic/addictive action, no antagonism action, against clinical isolates ofCRAB when treated with MFX+CFS. The SI of the30isolates treated with MFXor CFS alone are4~128and8~64respectively and reduce to1~8and4~16when treated with MFX+CFS, decreased2~16and2~4times respectively.2. Our results of PCR amplification showed that80%of30strains of CRABcarried two or more genes. Our gene sequencing results showed that genepoint mutations are present. For GyrA of MFX resistant-CRAB, there are fourtypes of mutations, including one kind of nonsense mutations; for parC, thereare14types of mutations, including6kinds of nonese mutations; for TEM ofCFS resistant-CRAB, there are one type of mutations.Conclusions1. These results suggest that the combination treatment of MFX+CFSagainst clinical isolates of CRAB might lower the MPC of the isolates treatedwith MFX/CFS alone, narrowing the mutant selection window, and preventingthe generation of drug-resistant mutants.2. Our results showed that the strains falling within the MSW are resistantto multi-gene, with new mutant subtypes found. Therefore, to limit thegeneration and enrichment of mutants, we need to seek effective treatmentregimens.