Cloning of a novel gene for quinolone resistance from a transferable plasmid in Shigella flexneri 2b

Abstract

A novel gene for quinolone resistance was cloned from a transferable plasmid carried by a clinical isolate of Shigella flexneri 2b that was resistant to fluoroquinolones. The plasmid conferred low-level resistance to quinolones on Escherichia coli HB101. The protein encoded by the gene showed 59% amino acid identity with Qnr.

FIG. 1.

Transmission of plasmid pAH0376 to E. coli HB101 and outbreak strains of S. flexneri 2b. Lanes: M, molecular size marker strain V517; 8, strain 8; HB101-T, transconjugant of HB101 with pAH0376 transmitted from strain 8; 5 and 7, strains 5 and 7; 5-T and 7-T, transconjugants of strains 5 and 7 with pAH0376 transmitted from HB101-T. The positions of plasmid pAH0376 and chromosomal DNA (Chr) are indicated on the right.

FIG. 2.

Alignment of deduced amino acid sequences of the ORF-encoded protein examined in this study (QnrS), Qnr, and hypothetical proteins of P. profundum (CAG22829) and V. vulnificus (AAO07889). Identical amino acids are highlighted.

FIG. 3.

Map of the EcoRI fragment of pAH0376. The qnrS gene and the TEM-1 β-lactamase gene are indicated. The other two open squares are the genes for resolvase (tnpR) and transposase (tnpA), respectively. The triangles represent 38-bp inverted repeats on both sides of the Tn3-like transposon. H, HindIII; R, EcoRI.