| Carbapenems are important class of β-lactam antibiotics, and often participate in antibiotic treatment of Acinetobacter baumannii infections. The carbapenem-resistant Acinetobacter baumannii has widely spread in China, which causing great difficulty in clinical thrapy. In order to formulate a scientific and effective prevention and control measures, different molecular typing method are used to study the epidemiological distribution and antibiotic resistance mechanisms of Acinetobacter baumannii.In this study,2197non-duplicated Acinetobacter baumannii were collected from64hospitals of23different provinces, and the susceptibility testing of12common antimicrobial agents were determined. According the results of susceptibility testing, we chose808strains of carbapenem-resistant Acinetobacter baumannii to perform Multilocus sequence typing (MLST) research. We applied Linux server, DNA fragment assembly tools and developed Perl scripts to achieve the batch processing of each allele sequencing data and identified the allele type with sequence type (ST). eBURST and Bionumerics software were used to analyze the data of MLST and predict the evolutionary relationships among different strains.The results of susceptibility testing revealed that the average resistance rate to12antibiotics in Acinetobacter baumannii were50%-60%, except minocycline only11.56%. The study of MLST data suggested that the genetic background of Acinetobacter baumannii was relatively simple, including40STs (17recorded by PubMLST database and23novel STs). ST92and its single locus variants (SLVs), ST138, ST75and ST381were the predominant STs. The results of eBURST and Bionumerics software demonstrated that the most widely disseminated Clonal complex (CC) of Acinetobacter baumannii was CC92in current China, and incorporate ST92, ST138and ST75et al. The study of susceptibility testing revealed that strains belonged to CC92with higher resistance compared to other STs. Results of this study indicated that CC92was the most widely spread and disseminated clonal complex in China, and often accompanied with the appearance and dissemination of multidrug resistance Acinetobacter baumannii. Hence, the widespread of CC92is the principal reason that responsible for the situation of antimicrobial resistance rate rose rapidly in Acinetobacter baumannii.Carbapenem-hydrolyzing class D β-lactamases (CHDLs) is the most commonly carbapenem in Acinetobacter spp., and often induce the mechanism of carbapenem resistance. In this study, we applied molecular biology method to discuss the relationship between the distribution of five OXA genes, which coding CHDLs, and dissemination mechanism in Acinetobacter spp.In this study,2880Acinetobacter spp. were collected from64hospitals of23different provinces, and the minimum inhibitory concentration (MIC) of12common antimicrobial agents were determined. We applied PCR-based amplified and sequencing technology to identify Acinetobacter spp., which harboring blaoxA-51-like,blaoXA-23-like, blaOXA-24-like, blaOXA-58-like and blaOXA-143-like gene, to the genus level. Pulsed-field gel electrophoresis (PFGE) and Southern blot hybridization were used to determine the location of OXA genes. Plasmid extraction and electrotransformation were applied to confirm the transferability of OXA carrying plasmids.Susceptibility testing indicated that the average resistance rate to carbapenem in Acinetobacter spp. were approximately50%. Results of multiplex PCR revealed that the proportion of Acinetobacter spp., which harboring biaOXA-51-like and biaOXA-23-like gene, were76.3%and45.7%respectively. Besides,44.9%of Acinetobacter spp. coharbor biaOXA-51-like and biaOXA-23-like gene, and up to95%of them resistant to carbapenems. The biaOXA-24-like, biaOXA-58-like and biaOXA-143-like gene were detected in32,11and1isolate(s) respectively. Southern blot hybridization indicated that the biaOXA-24-like, and biaOXA-58-like gene were located on plasmds, which can be transferred to recipient and increase its MIC values for carbapenems. But biaOXA-143-like gene can’t be detected by the method above, which indicated that it might be located on chromosome. |
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