ObjectiveTo analyze the homology of Citrobacter freundii strains and detect multidrug resistant genes.MethodsThe minimum inhibition concentration was tested with standard agar dilution method and the the homology of C.freundii strains was measured with pulsed field gel electrophoresis (PFGE) and the PCR was used to perform the drug resistant genes such as β-lactamase,disappearing of outer membrane channel protein.ResultsThe four strains ( No.1,2,4,5 ) showed nineteen banding patterns with PFGE.PCR experiment showed that there were 2 strains (No.1,4) with blaCTX-M,3 strains (No.2,3,5 ) with blaDHA,1 strains(No.3) with blaACT/MIR,and 4 strains(No.1,2,4,5) with blaKPC-2.PCR analysis comfirmed that No.2 and No.4 disappearing of OmpF and No.3 disappearing both of OmpC and OmpF.The expression levels of the chromosomal ampC gene of No.3 isolates was 106.7 times higher than the negative isolates.ConclusionThere is high homology in carbapenem-resistant isolates and the mechanism of drug resistance is complex including blaKPC,AmpC,ESBLs,disappearing of outer membrane channel protein.The spreading of drug resistance result from above genes.