Clonal spread of carbapenem resistant Acinetobacter baumannii ST92 in a Chinese Hospital during a 6-year period

The carbapenem resistance rate of Acinetobacter baumannii in our hospital has increased steadily since 2004. The molecular epidemiology of carbapenem resistant A. baumannii (CRAB) clinical isolates was characterized by multilocus sequence typing (MLST) and rep-PCR in parallel, with pan-drug susceptible A. baumannii (PSAB) used as control. MLST was performed to determine the sequence types (STs), and eBURST algorithm was used to analyze their relatedness. Carbapenem resistance related genes (oxa-23, oxa-24, oxa-51, oxa-58, imp, vim, and adeB) were screened using Polymerase Chain Reaction (PCR) method. 23 STs were identified in the 65 included isolates, with ST92 being the predominant clone. PSAB clustered into more singletons than CRAB. The positivity of oxa-23 and adeB correlated with high level carbapenem resistance (MICIPM > 32 mg/L, MICMEM > 32 mg/L) of CRAB ST92 isolates in 2009, which was different from the resistance pattern (MIC(IPM)a parts per thousand currency sign4 mg/L, 8 mg/L a parts per thousand currency signMIC(MEM)a parts per thousand currency sign16 mg/L) of CRAB ST92 isolates in 2004. These observations suggest that clonal spread of CRAB ST92 isolates longitudinally is the possible reason for carbapenem resistance rate increase and correlate with high level carbapenem resistance in our hospital.