Investigation On Epidemiology And Resistant Mechanisms To β-lactam Antibiotics Of Acinetobaeter Baumannii As Nosocomial Pathogens

Objective: To survey on the epidemiology, the drug-resistance and producing ofβ-lactamses of Acinetobacter baummanii in nosocomial infections and study on the resistant mechanisms and homology of carbapenem-resistant Acinetobacter baummani in order to provide the strategies of control of the prevalence and therapy in nosocomial infections of Acinetobacter baummanii.Methods: We retrospectively analysed the data of 98 Acinetobacter baumannii isolates from the inpatients of two hospitals in Bengbu. Drug sensitivity analysis was conducted by WHONET 5.4 software to clarify its infection status and the rates of antibiotic resistance. 98 Acinetobacter baummanii strains were screened forβ-lactamases by Nitrocefin. A modified three-dimensional extract test and the double-disc diffusion test were used to detect phenotypically isolates which produced AmpCβ-lactamases, extended-spectrumβ-lactamases and metal-beta-lactamase. Gene fragments encoding carbapenemase including blaOXA, IMP and VIM were detected by PCR, for definite genotypes, their full length genes were further amplifed and sequenced. The homology of the isolates was determined by pulsed field gelel ectrophoresis (PFGE).Results: The Acinetobacter baummanii infections associated morbidity was high in our district, particularly in ICU wards, orthopedics wards then was neurosurgery wards. Except imipenem was 64.29%, the resistance rates of Acinetobacter baummanii various of antibiotics were 65%-90%. Among 98 strains of Acinetobacter baumanii producing beta-lactamase bacteria accounted for 94(95.92%); producing AmpC enzyme bacteria accounted for 58(59.18%); producing ESBLs bacteria accounted for 9(9.18%).Genetype analysis of the carbapenemase showed that 48 strains blaOXA-64-liuke,24 strains blaOXA23 and 3 strains blaOXA58 were found, whereas other genes were negative in 63 strains of Immpeinem-resistant Acinetobacter baumanii. Forty-six strains isolated from the first affiliated hospital of Bengbu medical college were classified into type A, B and C based on PFGE pattern. Of these, 41 strains of type A were the dominant strains including subtypes A1(32/41),A2(8/41) and A3(1/41), the remaining isolates belonged to two additional types: 3 to type B and 2 to type C. 4 strains out of 17 from Bengbu Central Hospital were consistent with A1 lane from the first affiliated hospital of Bengbu Medical College. The remaining 13 strains belonged to type D and type E: 11 type D strains including subtypes D1(9/11),D2(2/11) and 2 type E strains.Conclusions: There is a high morbidity of Acinetobacter baummanii nosocomial infections in our district. The resistance toβ-lactam antibiotics is mainly due to highβ-lactamase produced by Acinetobacter baumannii. Production of OXA-51 and OXA-23 carbapenemase in Acinetobacter baumanii is one of the main mechanisms of imipenem-resistance in Bengbu district. Results of PFGE show there are cross infections among wards, departments and hospitals.