engleski

Emergence of three different Acinetobacter baumannii clones in general hospital Pula, Croatia

Objectives An increase in the prevalence of carbapenem resistant A.baumannii was observed in General Hospital (GH) in Pula. Three clones of A. baumannii based on routine antimicrobial susceptibility testing were observed: one cluster susceptible, the second intermediate susceptibile and the third resistant to carbapenems. Methods In total 60 A. baumannii strains were analyzed: 9 strains susceptible to carbapenems, 14 intermediate susceptibile and 27 strains resistant to carbapenems. The isolates were collected from June 2013 till June 2014. Antimicrobial susceptibility testing was performed by broth microdilution method. PCR was used to detect genes encoding carbapenemases of group A, B (MBL-metallo-β-lactamases) and D (CHDL) and extended-spectrum β-lactamases (ESBL). Epidemiologic typing was performed by determination of sequence groups (SG). Results The first group of strains susceptible to carbapenems (9 strains) showed resistance cefotaxime and ceftriaxone. All strains were susceptible to ceftazidime, cefepime, piperacillin/tazobactam, ampicillin/sulbactam gentamicin, amikacin, tigecycline and colistin. PCR revealed only the presence of blaOXA-51 gene without ISAba1. The second group of strains were intermediate susceptible to carbapenems (24 strains). All were resistant to expanded-spectrum cephalosporins (ESC), piperacillin/tazobactam and ciprofloxacin. 96% of the strains were resistant to cefepime and 50% to gentamicin. The strains were uniformly susceptible to ampicillin/sulbactam, amikacin, tigecycline and colistin. Amikacin demonstrated good activity with 96% susceptible strains. PCR detected only blaOXA-51 gene upregulated by ISAba1. The third group contained 27 strains resistant to carbapenems. The strains were uniformly resistant to ESC, piperacillin/tazobactam, ciprofloxacin and gentamicin, but uniformly susceptible to ampicillin/sulbactam, tigecycline and colistin. In contrast to first and second group, the strain in the third group were positive phenotypically for MBLs but negative for ESBLs. All strains harboured acquired CHDL and MBL belonging to the VIM family. Out of 27 strains, 20 harboured blaOXA-24-like, 4 blaOXA-58-like and 3 blaOXA-23-like genes. The strains belonging to groups 1 and 2 belonged to SG 2 while strains resistant to carbapenems in the third group were allocated to SG 1. Conclusions The study demonstrated existence of three different clones of A. baumannii in GH Pula. The previous study conducted in 2009-2010 showed that reduced susceptibility to carbapenems in GH Pula was only associated with upregulation of intrinsic OXA-51 β-lactamase by ISAba1 located upstream of blaOXA-51 gene. In this study shift to acquired CHDL and MBLs was reported. Genotyping of the isolates is necessary to determine if the resistant strains harbouring acquired CHDL and MBL were imported from other hospital centers in Zagreb where they were previously identified or they arose de novo.

Acinetobacter baumannii ; carbapenemase ; OXA-23

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