Prevalence of different carbapenemase genes among carbapenem-resistant Acinetobacter baumannii blood isolates in Taiwan

Abstract

Background: Although the prevalence of the carbapenem-resistant A. baumannii (CRAB) has increased in Taiwan, few studies have elucidated the prevalence of different carbapenemase genes in Taiwan. The first objective of this study was to identify the types and prevalence of different carbapenemase genes, and the second objective was to determine the carbapenem antimicrobial susceptibility of carbapenemase producing isolates.

Methods: In total, 269 CRAB blood isolates from four medical centres in Taiwan from 1/1/2009 to 31/12/2013 were analysed. Antimicrobial susceptibilities were determined using the Vitek 2 system. Carbapenemase genes were identified by polymerase chain reaction (PCR) and sequencing. Pulsed-field gel electrophoresis (PFGE) was used to identify the different pulsotypes.

Results: All 269 CRAB isolates had the bla_OXA-51-like gene, while 237 (88.1%) had the bla_OXA-23-like gene, and 11 (4.09%) had the bla_OXA-24-like gene. Twenty-one CRAB isolates (7.81%) contained only the bla_OXA-51-like gene. None of the isolates had the bla_OXA-58-like gene or the metallo-β-lactamases (MBL)-encoding genes. In 28.69% of isolates with the bla_OXA-23-like gene and 90.91% of isolates with the bla_OXA-24-like gene, the minimum inhibitory concentrations (MICs) for imipenem were 64 mg/L or more. In 37.55% of isolates with the bla_OXA-23-like gene and 100% of isolates with the bla_OXA-24-like gene, meropenem MICs were 64 mg/L or more. PFGE analyses indicated that six highly similar genomes which harbored the bla_OXA-24-like gene came from three different medical centres.

Conclusion: Our study determined the prevalence of CRAB, the types and prevalence of carbapenemase genes, carbapenem susceptibility among CRAB isolates, and documented that the bla_OXA-24-like gene had greater resistance to carbapenem than the bla_OXA-23-like gene. We also demonstrated inter-hospital transmission of the highly resistant bla_OXA-24-like gene.

Keywords: Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB) complex; Carbapenem-resistant Acinetobacter baumannii (CRAB); blaOXA-23-like; blaOXA-24-like; blaOXA-51-like.

Fig. 1

Distribution of imipenem MICs in 269 CRAB blood isolates with the bla_OXA-23-like and bla_OXA-24-like genes

Fig. 2

Distribution of meropenem MICs in 269 CRAB blood isolates with the bla_OXA-23-like and bla_OXA-24-like genes

Fig. 3

Pulsed-field gel electrophoresis results of A. baumannii isolates that had the bla_OXA-24-like and bla_OXA-51-like genes. There were 11 distinct genospecies and 3 PFGE dominant types. The scale indicates the percentage of overall genetic similarity. Isolates with the same letter were from the same hospital. M1, M2, M3, C5, C6, and V1 with the same gene cluster came from 3 different hospitals. Letter C: Changhua Christian Hospital. Letter M: MacKay Memorial Hospital. Letter V: Taipei Veterans General Hospital