Complex Class 1 Integron Carrying qnrB62 and blaVIM-2 in a Citrobacter freundii Clinical Isolate

Abstract

The coexistence of qnrB62 and bla_VIM-2 was detected in a Citrobacter clinical isolate. The reduced fluoroquinolone susceptibility is attributable to qnrB62, mutations of quinolone-resistance-determining regions, and an 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 (bla_VIM-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.

FIG 1

(a) Southern blotting of I-CeuI-digested genomic DNA of C. freundii 11-7F4560 carrying the qnrB62 gene. Lanes: M, lambda ladder PFGE marker (Bio-Rad); 1, I-CeuI restriction banding pattern of genomic DNA from C. freundii 11-7F4560 carrying the qnrB62 gene; 2, Southern blotting of genomic DNA with a probe specific to the 16S rRNA gene; 3, Southern blotting of genomic DNA with a probe specific to the qnrB62 gene. The band containing the qnrB62 gene is marked with an arrow. (b) The genetic map of chromosomal DNA from C. freundii 11-7F4560 carrying qnrB62 located a new complex class 1 integron (In1184::ISCR1::qnrB62), C. freundii F2503 carrying qnrB35, C. freundii S50552 carrying qnrB38, C. braakii ATCC 51113^T carrying qnrB61 and five different integrons (In886 from P. aeruginosa YMC/MJ0820, In1008 from P. aeruginosa 81-11963A, In852 from C. freundii S1-1, In38 from C. freundii, and In432 in plasmid pK097 from E. coli 97). Genes are represented by arrow boxes. Genes identified in In1184 are bla_VIM-2 (encoding metallo-β-lactamase VIM-2), aacA4′-8 [encoding aminoglycoside (6)′-N-acetyltransferase], gucD (open reading frame of a gene of unknown function), pspA(Δ18) (phage shock protein A gene with an 18-nucleotide 3′ deletion), pspF (encoding phage shock protein F), and qnrB62 (encoding a quinolone resistance determinant). The 5′-CS and 3′-CS are indicated by white arrow boxes. Vertical black bars represent IRR2. The constant (or similar) regions are indicated by gray shading. In an enlargement of the region between the recombination crossover site (RCS) and pspA(Δ18), the RCS is underlined. oriIS (the initiation site of ISCR1 transposition) is boxed and underlined. Δ18 (dotted line box) is an 18-nucleotide 3′ deletion (dashed lines) in a 691-bp open reading frame encoding PspA.