In Vitro Activity And Resistance Mechanism Study Of Fosfomycin Against K.pneumoniae Carbapenemases-klebsiella Pneumoniae

Objective:This paper was designed to evaluate the activity of both single Fosfomycin and combinations against K.pneumoniae carbapenemases-Klebsiella Pneumoniae through susceptibility testing,combined susceptibility and time-killing experiments.we determined mutant prevention concentration(MPC)of Fosfomycin,colistin and tigecycline to evaluate their potential to restrict resistance.Futhermore,we sequenced MurA,glpT and uhpT genes derived from resistant strains.Methods:The MICs of fosfomycin was determined by the agar dilution method.Based on the MICs and pharmacokinetic/pharmcodynamic indices,combined susceptibility tests and time-killing experiments were performed to evaluate the efficacy of fosfomycin,colistin and tigecycline both alone and in combinations.Furthmore,we determined MPC of Fosfomycin,colistin and tigecycline both alone and and combinations against Fosfomycin susceptible strains.Finally,we uesed PCR to determined potential resistance mechanism for Fosfomycin by sequencing MurA,glpT and uhpT genes.Result:The MICs results showed 35.71%of 70 isolates were susceptible to Fosfomycin.In combined susceptibility test.20%isolates show FIC<0.5 for Fosfomycin and colistin while 52%isolates FIC is between 0.5 and 1.isolates FIC is 16%,and the FIC of rest isolates is between 1 and 2.as for Fosfomycin and tigecycline,8%isolates’ FIC<0.5,64%isolates’ 0.5<FIC<1,20%isolates’ FIC=1,8%isolates’ FIC is 1 and 2.In time-killing experiment,Fosfomycin and colistin showed most effective antimicrobials activity among all agents and combinations.The MPC range of fosfomycin is>2048mg/L,the MPC range of colistin is 64-256mg/L,and the MPC range of tigecycline is 4-32mg/L.Mutants in MurA,uhpT,glpT genes were found in Fosfomycin resistance strains selected by MPC experiments.Conclusion:(1)Clinically isolated 70 strains of KPC-KP have certain antibacterial activity against fosfomycin.(2)The results of combined drug susceptibility showed that fosfomycin and polymyxin E and tigecycline showed synergistic effects on most KPC-KP strains,and they showed additive or unrelated effects on some strains,with no antagonism.The time bactericidal curve found that the bactericidal effect of fosfomycin combined with polymyxin E or tigecycline was better than monotherapy,and the bactericidal effect of fosfomycin combined with polymyxin E was best.(3)Fosfomycin,polymyxin E,tigecycline single drug MPC high and blood drug concentration,MSW is too wide,single application is susceptible to drug resistance.When fosfomycin was combined with polymyxin E or tigecycline,the decrease in MPC was not significant,and combined drug use was not ideal for limiting drug resistance.(4)KPC-KP resistance to fosfomycin is associated with mutations in MurA,uhpT and glpT genes.