Study On The Resistance Mechanisms And Molecular Epidemiology Of Carbapenem-resistant Acinetobacter Baumannii

Objective：To investigate the resistance mechanisms and molecular epidemiologicalof carbapenem-resistant acinetobacter baumannii isolated from blood specimens ofbloodstream infections patients in Beijing haidian hospital and Peking UnionMedical College Hospital for clarifying the mechanism of resistance andunderstanding epidemiological characteristics, and providing the scientific basis forprevention and treatment to control the spread of resistant strains in hospital.Methods：A total of150nonduplicate strains of acinetobacter baumannii(including137isolates of carbapenem-resistant and13isolates of carbapenem-susceptibility) in83patients of BSI were collected from different body sites between January2009and October2010in Beijing haidian hospital and Peking Union Medical CollegeHospita, which including blood83strains, respiratory tract (sputum and bronchialaspirates)54strains, catheter tip s4strains and other site specimens(drainage fluid,bile, urine and so on)9strains. Antimicrobial susceptibility testing was carried outby means of Kirby-Bauer method according to the unified protocol, Thecarbapenemase gene were amplified by PCR and its products were sequenced.Epidemiological genotyping of acinetobacter baumannii strains were analyzed bypulse-field gel electrophoresis(PFGE) and multilocus sequence typing(MLST). Andinvestigating the bloodstream infectinons patients’ clinical data.Results：A total of150nonduplicate strains of acinetobacter baumannii were isolatedfrom different body sites of BSI patients, which142isolates were multidrug-resistant (accounting for94.7%) and20isolates were pandrug-resistant (accountingfor13.3%). All strains maintained very high resistant rate(more than73.3%) to16antimicrobial agents except minocycline (36.7%). The detection of carbapenemasegene showed that among150aba strains, All aba strains carried blaOXA-51-likegene,133strains (88.7%)carried blaOXA-23-likegene, other carbapenemase gene were notdetected. For MLST type,150Aba strains were divided into ten ST types(7strainswere not detected): ST208, ST218, ST368-375, which ST208, ST368and ST370were the most popular ST type in Peking Union Medical College Hospital, while Beijing haidian hospital were ST370and ST218, and ST368to ST375are describedhere for the first time; While for PFGE type, these strains were divided into15type(A-O), type A and B were the most popular type in Peking Union MedicalCollege Hospital and Beijing haidian hospital was type A and C. We analysised theclinical date of patients and found that the mortality rate of BSI was45.2%, theaverage age was60.8years old, and mainly in the ICU.62.9%patients wereaccompanied by pulmonary infection, and29.0%were accompanied by more thanone site infection besides lung;79.0%patients experienced more than one invasiveprocedures before BSI; All patients received at least one antibiotic therapy, which69.4%patients used more than three antibiotics.Conclusion：OXA-23was the main mechanism of acinetobacter baumannii forcarbapenem resistance in the present study; and suggested that it exist clonal spreadamong hospitals, departments or patients in the same department; See from theMLST or PFGE type of the same patient from different parts(such as blood andsputum, blood and bile, blood and renal pelvis drainage fluid and so on), we canknow that the vast majority strains were the same clone, which suggesting theprimary disease can cause BSI mostly, mainly lung infection.