What is it about?
We present here (i) the first report of the complex class 1 integron that simultaneously carries blaVIM-2 and a new qnrB allele (qnrB62) in a Citrobacter clinical isolate resistant to fluoroquinolones and carbapenems, (ii) other mechanisms responsible for fluoroquinolone resistance, and (iii) potential horizontal spread of qnrB62 (or blaVIM-2) gene.
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Why is it important?
The coexistence of qnrB62 and blaVIM-2 was detected in a Citrobacter clinical isolate. The reduced fluoroquinolone susceptibility is attributable to qnrB62, mutations of quinolone-resistance-determining regions, and efflux pump or pumps. The genetic context surrounding chromosomal qnrB62 was a novel complex class 1 integron (In1184::ISCR1::qnrB62) containing a unique gene array (blaVIM-2-aacA4’-8-gucD). An 18 nucleotide deletion at the 3′ end of the pspA gene [pspA(Δ18)], upstream of qnrB62, and an inverted repeat region (IRR2) were detected in In1184::ISCR1::qnrB62, indicating past transposition events.
Perspectives
PCR-based detection of QRDR mutations identified a Thr83Ile substitution in GyrA, a Phe431Ser substitution in GyrB, and a Ser80Ile substitution in ParC. The Thr83Ile and Ser80Ile substitutions are sufficient for decreased fluoroquinolone susceptibility in Citrobacter isolates and E. coli isolates, respectively. However, Phe431Ser in GyrB is a novel substitution in the Citrobacter isolates and the significance of this mutation is unclear. MIC of all-tested (fluoro)quinolones varied by more than 4-fold in the presence of the efflux pump inhibitor Phe-Arg-β-naphthylamide, suggesting variable contribution of an efflux pump or pumps in determining quinolone susceptibility. However, plasmid-mediated qepA, oqxA, and oqxB genes were not detected in C. freundii 11-7F456011, suggesting the involvement of chromosomal efflux pumps (e.g., intrinsic RND type efflux pumps) other than QepA or OqxAB in the reduced quinolone susceptibility of the C. freundii isolate. Further study is needed to define the actual roles of the Phe431Ser mutation in
Professor Sang Hee Lee
Myongji University
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This page is a summary of: Complex Class 1 Integron CarryingqnrB62andblaVIM-2in a Citrobacter freundii Clinical Isolate, Antimicrobial Agents and Chemotherapy, August 2016, ASM Journals,
DOI: 10.1128/aac.00614-16.
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