Dissemination and Genetic Structure of Carbapenemase Encoding Genes (bla<sub>OXA-23</sub> and bla<sub>OXA-24</sub>) in <i>Acinetobacter baumannii</i> from Southern Texas

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.

Draft Genome Sequences of Clinical Isolates of Multidrug-Resistant Acinetobacter baumannii

“…The 13 resistance genes found include two aminoglycosides ( strA and strB ), eight β-lactams (ADC-76, blaA1 , blaA2 , mbl , OXA-24, OXA-65, TEM-116, and a zinc-dependent hydrolase), two chloramphenicols ( catA1 and cmlB1 ), and one sulfonamide ( sulII ). OXA-24 is the only gene not on the genome; it appears to be on a plasmid, similar to GenBank JN207494.1 (4). …”

“…A. baumannii is a decidedly adaptive species, demonstrating a wealth of mechanisms for evading diverse antibiotic classes, including on horizontally transferred resistance islands in the genome (2, 3) and resistance-conferring plasmids (4). A. baumannii is also able to survive for extended durations on dry surfaces (5).…”