Molecular analysis of beta lactamases in clinical Acinetobacter baumannii isolates from intensive care units

Thesis Type: Doctorate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Arts and Sciences, Department of Biology, Turkey

Approval Date: 2011


Supervisor: AYŞE GÜL GÖZEN


Carbapenem resistance in Acinetobacter baumannii is a growing public health concern and represents a serious problem for treatment of the infection. Several carbapenem-hydrolysing β-lactamases have been identified from A. baumannii so far. In this study carbapenem resistance in A.baumannii strains recovered from intensive care units of Gulhane Military Medical Academy, Turkey, were investigated via multiplex PCR and with parallel phenotypic tests. From June 2006 to January 2010, 138 clinical A. baumannii isolates were collected. Identification and antimicrobial susceptibility tests of the isolates were performed. The MICs of imipenem and meropenem were determined by using E-test method. Carbapenem resistant A. baumannii strains were included for further study. Firstly, the presence of carbapenemases were determined. The presence of Metallo-beta-lactamase (MBL) were also investigated. Detection of the four groups of OXA carbapenemases (OXA- 23, OXA-24, OXA-51 and OXA-58) was carried out using a multiplex PCR assay. Sequence analyses were performed. Non-duplicate, multidrug resistant 61 clinical A. baumannii isolates were found to be resistant to imipenem and meropenem. In the 61 isolates, the MIC50 of imipenem and meropenem were 16 and >32; MIC90 were 192 and >32 respectively. Modified Hodge Tests (MHT) were positive for all 61 A. baumannii strains. None of these isolates showed MBL activity. As determined through multiplex PCR, all of the 61 isolates had blaOXA-51 genes, 50 isolates had blaOXA-23, and 11 isolated had blaOXA-58 genes. Alleles encoding OXA-24-like enzymes were not detected in any isolates. This study indicated that the clinical isolates in our region contained blaOXA-51, blaOXA-23, and blaOXA-58 resistance genes. However, blaOXA-24 gene was either absent or occur in very low frequency.