Investigation of oxa type beta-lactamases and pfge patterns in acinetobacter baumannii strains resistant to carbapenems

Acinetobacter baumannii is an important opportunistic and multidrug-resistant pathogen leading to nosocomial infections. Over the last 10 years, a significant and threatening increase in resistance to carbapenems, mainly due to the dissemination of class D beta-lactamases, has been reported in A.baumannii worldwide. The most common types of beta-lactamases causing carbapenem resistance in A.baumannii are the OXA-23, OXA-24, OXA-4C), OXA-58 and OXA-143 type serine beta-lactamases. The aim of this study was to investigate the presence of OXA type beta-lactamases in carbapenem-resistant A.baumannii strains and the clonal relationship between the strains. A total of 105 non-duplicate carbapenem-resistant A.baumannii strains isolated from various clinical samples (68 blood, 18 bronchoalveolar lavage, 13 drainage, 3 urine, 2 cerebrospinal fluid and 1 catheter samples) in the Microbiology Laboratories of Selcuk University, Meram (2009-2012) and Selcuklu (2007-2008) Medical School Hospitals, were included in the study. The isolates were identified by conventional methods and Phoenix 100 BD (BD Diagnostic, USA) and Vitek II (bioMerieux, France) automated systems. Carbapenem susceptibility test was performed by Kirby-Bauer disk diffusion method according to the CLSI standards. blaOXA23.like' blaOXA 24-like' blaOXA 58-like and blaOXA 51-like genes were amplified by multiplex PCR assay and clonal relatedness was investigated by pulsed-field gel electrophoresis (PFGE) using Apal enzyme. The blaOXA 51-like gene was determined in all carbapenem-resistant A.baumannii isolates, while the blaOXA 23-like and blaOXA 58-like genes were detected in 46.6% and 53.3% of isolates, respectively. However blaOXA 24-like gene was not demonstrated in any isolates. blaOXA 23-like gene was determined in both Meram and Selçuklu Medical School hospitals, but blaOXA 58-like gene was detected only in Meram Medical School hospital. PFGE analysis of the isolates revealed 32 different groups in blaOXA 23-like producing A.baumannii strains and 23 different groups determined in blaOXA 58-like producing strains. No common epidemic isolates were detected in the two hospitals, however it was noted that some clones produced small outbreaks in Meram MS hospital. In this study it was shown that blaOXA 23-like and blaOXA 58-like genes together with blaOXA 51-like gene had significant roles in the carbapenem-resistance of A.baumannii strains. Carbapenem-resistant A.baumannii strains producing blaOXA 23-like and blaOXA 58-like enzymes showed the epidemic potential of this nosocomial pathogen and the requirement of molecular typing methods to identify the epidemiologic relationship of the isolates.