[Molecular epidemiology and resistance mechanisms of tigecycline-non-susceptible Acinetobacter baumannii]

To investigate the resistance mechanisms of tigecycline-non-susceptible Acinetobacter baumannii and for providing the evidence of the control of nosocomial infection and rational use of antibiotics. The minimum inhibitory concentrations (MICs) of 94 non repetitive tigecycline-non-susceptible A. baumannii from 20 hospitals in 12 cities of China were determined by agar dilution method and broth microdilution method. The molecular epidemiology was studied by Multilocus sequence typing (MLST) and eBURST software. PCR and sequencing techniques were used to analyze the resistance genes (blaOXA-40-like, blaOXA-58-like, blaOXA-23-like, blaOXA-51-like, blaNDM-1), ISAba1, and the mutation sites of adeR, adeS, and trm. The activity of polymyxin B and minocyclinem against tigecycline-non-susceptible A. baumannii were 100% and 25.5%, respectively. The sensitivities of other antibiotics were less than 3.5%, and the sensitivities of imipenem and meropenem totigecycline-nonsusceptible A. baumannii were only 1.1%. A total of 12 ST types were identified, including ST195 (45, 47.9%), ST208 (19, 20.2%) and ST457 (10, 10.6%). EBURST analysis found that 8 of the ST types belonged to the clone complex 92 (Clonal Complex 92, CC92). The blaOXA-23-like type carbapenem gene was identiefied in 93 strains (99% positive); and none of the strains contained the blaNDM-1 gene. The detection rates of adeR and adeS were 73.4% and 91.5% respectively and high frequency mutation sites were located in adeR (Asp26Asn) and adeS (Ala97Glu); The ISAba1 located upstream of the adeS gene was detected in 12 strains of A. baumannii, mainly from the northern region of China. The 240 nucleotide deletion of the trm gene caused a frameshift leading to a premature stop. So the tigecycline-non-susceptible A. baumannii showed high resistance against most antibiotics except polymyxin B. The deletion and mutation of adeR, adeS and trm were the main resistant mechanisms in tigecycline-non-susceptible A. baumannii in China.