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Volume 48, Number 1, February 2015

Evolution of carbapenem resistance in Acinetobacter baumannii: An 18-year longitudinal study from a medical center in northern Taiwan 


Wen-Wei Ku, Che-Hsuang Kung, Chi-Hung Lee, Chih-Peng Tseng, Ping-Feng Wu, Shu-Chen Kuo, Te-Li Chen, Yi-Tzu Lee, Fu-Der Wang, Chang-Phone Fung


Received: April 30, 2013    Revised: June 13, 2013    Accepted: July 16, 2013   

 

Corresponding author:

* Corresponding author. Department of Emergency Medicine, Taipei Veterans General Hospital, Number 201, Section 2, Shih-Pai Road,
Taipei 112, Taiwan.
E-mail address: yitzulee@gmail.com (Y.-T. Lee). 



 

Background and purpose: 

Carbapenem-resistant Acinetobacter baumannii has emerged as an important cause of nosocomial infections with high morbidity and mortality. The carbapenemases, especially class D carbapenem-hydrolyzing oxacillinases (CHDLs), play an important role, but the relationship between their prevalence trend and carbapenem resistance remains unclear. 



 

Methods:

Between 1995 and 2012, we collected 667 isolates of A. baumannii from a single medical center in northern Taiwan. Pulsed-field gel electrophoresis (PFGE) was used to determine clonality. Antimicrobial susceptibility was determined. Carbapenemase genes and associated genetic structures were detected by polymerase chain reaction.
 



 

Results:

Isolates were heterogeneous on PFGE. Susceptibility to carbapenem decreased steadily over the study period from 88.1% (2001–2003) to <25% (2010–2012), whereas the isolates remained susceptible to colistin (nearly 100%) and partially susceptible to tigecycline (80%). Starting in 2001, isolates carrying the ISAba1-blaOXA-51-like allele were consistently identified. Isolates containing the transposons Tn2006 or Tn2008 first appeared in 2007 with increasing carriage rates from 17.5% (2007–2009) to 50.0% (2010–2012). The IS1008-ΔISAba3-blaOXA-58-like, blaOXA-72 and metallo-β-lactamase genes were detected only sporadically. Isolates carrying CHDL genes were resistant to multiple drugs, including carbapenem, but remained susceptible to colistin (100.0%). 



 

Conclusion:

Increased carbapenem resistance in A. baumannii may be caused by the increased prevalence of isolates containing the ISAba1-blaOXA-51-like allele and the transposons Tn2006 and Tn2008. 



 

Key words:

ISAba1-blaOXA-23-like, ISAba1-blaOXA-51-like, Tn2006, Tn2008