Evolution of carbapenem resistance in Acinetobacter baumannii: an 18-year longitudinal study from a medical center in northern Taiwan.
BACKGROUND
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%).


CONCLUSIONS
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.
Division of Infectious Diseases, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan.
Wen-Wei
WW
Ku
Division of Infectious Diseases, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan.
Che-Hsuang
CH
Kung
Division of Infectious Diseases, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan.
Chi-Hung
CH
Lee
Division of Infectious Diseases, Department of Medicine, Cheng Hsin General Hospital, Taipei, Taiwan.
Chih-Peng
CP
Tseng
Division of Infectious Diseases, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan.
Ping-Feng
PF
Wu
National Institute of Infectious Diseases and Vaccinology, National Health Research Institute, Maoli County, Taiwan; School of Medicine, National Yang Ming University, Taipei, Taiwan.
Shu-Chen
SC
Kuo
School of Medicine, National Yang Ming University, Taipei, Taiwan.
Te-Li
TL
Chen
School of Medicine, National Yang Ming University, Taipei, Taiwan; Department of Emergency Medicine, Taipei Veterans General Hospital, Taipei, Taiwan. Electronic address: yitzulee@gmail.com.
Yi-Tzu
YT
Lee
Division of Infectious Diseases, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan; School of Medicine, National Yang Ming University, Taipei, Taiwan.
Fu-Der
FD
Wang
Division of Infectious Diseases, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan; School of Medicine, National Yang Ming University, Taipei, Taiwan.
Chang-Phone
CP
Fung
D000046:Academic Medical Centers; D000151:Acinetobacter Infections / Q000453:epidemiology / Q000382:microbiology*; D040981:Acinetobacter baumannii / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015780:Carbapenems / Q000494:pharmacology*; D016000:Cluster Analysis; D003428:Cross Infection / Q000453:epidemiology / Q000382:microbiology; D004251:DNA Transposable Elements; D016521:Electrophoresis, Gel, Pulsed-Field; D005798:Genes, Bacterial; D005838:Genotype; D006801:Humans; D008137:Longitudinal Studies; D008826:Microbial Sensitivity Tests; D017720:Molecular Epidemiology; D058889:Molecular Typing; D015995:Prevalence; D013624:Taiwan / Q000453:epidemiology; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics
D000900:Anti-Bacterial Agents; D015780:Carbapenems; D004251:DNA Transposable Elements; D001618:beta-Lactamases
ISAba1-bla(OXA-23-like); ISAba1-bla(OXA-51-like); Tn2006; Tn2008