Ann Lab Med.  2012 Nov;32(6):413-419.

Clonal Spread of Carbapenem Non-susceptible Acinetobacter baumannii in an Intensive Care Unit in a Teaching Hospital in China

• Zhong Q
• Xu W
• Wu Y
• Xu H

Abstract

BACKGROUND
This study was aimed to investigate the genetic diversity and antibiotic resistance profile of the nosocomial infection agent Acinetobacter baumannii from a medical intensive care unit (ICU) in a teaching hospital in Suzhou, China.
METHODS
The genetic relationship among A. baumannii isolates in an ICU was investigated using multilocus sequence typing (MLST). The antibiotic resistance pattern was determined by performing an antibiotic susceptible test, which included an agar dilution method and an E-test method. Resistant determinants, e.g., carbapenemase genes, metallo-beta-lactamases, and class 1 integron, were analyzed by specific PCR and DNA sequencing.
RESULTS
In the present study, 33 non-duplicate isolates were identified as 5 existing sequence types (STs) (ST92, ST75, ST112, ST145, and ST345) and 1 new sequence type STn, which has a G-A mutation at nt268 on ropD40 of ST251. These results reveal limited diversity in carbapenem non-susceptible A. baumannii (CNSAb) isolates in our ICU, which are comprised of only 2 distinct STs, with ST92 and ST75 clustering into a clonal complex (CC) 92. Most CNSAb isolates (94.4%, 17/18) harbored the OXA-23 gene, while no carbapenem-susceptible A. baumannii (CSAb) isolates harbored it. In addition, 66.7% (22/33) isolates were positive for class 1 integrase, and gene cassette analysis showed there are 3 gene arrays among them, i.e., aacA4-catB8-aadA1 (77.3%, 17/22), aacA4 (22.7%, 5/22), and aacC1-orfX-orfX'-aadA1 (4.5%, 1/22).
CONCLUSIONS
When all these data are combined, the antibiotic resistance and wide distribution of CNSAb isolates in our ICU are probably caused by expansion of the CC92 clone.

Keyword

MLST; Molecular epidemiology; Acinetobacter baumannii

MeSH Terms

Acinetobacter baumannii/*drug effects/enzymology/genetics/isolation & purification
Anti-Bacterial Agents/*pharmacology
Bacterial Proteins/genetics
Carbapenems/*pharmacology
China
Drug Resistance, Bacterial/drug effects
Hospitals, Teaching
Humans
Integrases/genetics/metabolism
Intensive Care Units
Microbial Sensitivity Tests
Mutation
Polymerase Chain Reaction
Sequence Analysis, DNA
beta-Lactamases/genetics
Anti-Bacterial Agents
Bacterial Proteins
Carbapenems
Integrases
beta-Lactamases

Figure

• 

  Fig. 1 Population structure of Acinetobacter baumannii in this study and an existing isolate in China, represented by an eBURST algorithm. A circle represents an ST, and its size corresponds to the number of isolates. The broken line indicates clonal complex (CC) 92. ST112, ST145, ST345, and STn1 are the singletons in this study. ST represents sequence type, i.e. ST92, 1-3-3-2-2-7-3, ST75, 1-3-3-2-2-11-3, ST112, 1-12-56-36-4-61-26, ST145, 21-35-2-28-1-52-4, ST345, 46-12-110-1-16-141-50, and STn1, representing a new sequence type with a G-A mutation at nt268 on the rpoD40 loci of ST251(32-48-54-35-1-11-40); CC represents clonal complex.

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