TITLE:
Dissemination and Genetic Structure of Carbapenemase Encoding Genes (blaOXA-23 and blaOXA-24) in Acinetobacter baumannii from Southern Texas
AUTHORS:
Nidha Azam, Tamanna Talukder, Kava R. Robinson, Dong H. Kwon
KEYWORDS:
Acinetobacter baumannii, Dissemination and Genetic Structure of Carbapenemase-Encoding Genes
JOURNAL NAME:
Advances in Microbiology,
Vol.5 No.6,
June
29,
2015
ABSTRACT: Acinetobacter baumannii is one of the most important human
pathogens causing a variety of nosocomial infections. Carbapenem antibiotics
have been primarily used to treat the A.
baumannii infections. However, carbapenem resistant A. baumannii producing carbapenemases causes serious treatment
problems worldwide. Outbreaks of carbapenem resistant isolates have reported in
some area of the United States, but their dissemination and genetic structure
of the carbapenemase encoding genes are currently little known. To understand
outbreaks, dissemination, and genetic structure of the carbapenemase encoding
genes in Southern Texas, 32 clinical isolates collected from Austin and Houston,
TX were characterized. Twenty-eight of 32 isolates were resistant to all tested β-lactam
antibiotics including carbapenem (imipenem
and meropenem). Three of them carried blaOXA-23 as a part of Tn2008 integrated into a known plasmid (pACICU2) and all others
carried blaOXA-24 flanked
by XerC/XerD-like recombinase binding sites that were adjoined by DNA sequences
originated from multiple plasmids. Genotype analysis revealed that the 25
isolates carrying blaOXA-24 were all identical genotypes same as a representative isolate carrying blaOXA-24 from Chicago, IL
but the 3 isolates carrying blaOXA-23 was a distinct genotype as compared with isolates carrying blaOXA-23 from Chicago, IL and Washington, D.C. Each of
the blaOXA-23 and blaOXA-24 was transferred to
carbapenem susceptible A. baumannii and E. coli with similar minimal
inhibitory concentration (MIC) of carbapenem as that of their parental isolates
but significantly lower levels of MIC in E.
coli. Overall results suggest that a unique strain carrying blaOXA-23 and a similar
strain carrying blaOXA-24 as
seen in other geographic areas are currently disseminated in Southern Texas.