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.

Unexpected Occurrence of Plasmid-Mediated Quinolone Resistance Determinants in EnvironmentalAeromonasspp.

“…As opposed to most qnrA and qnrB genes, qnrS genes have never been reported to be associated with sul1-type class 1 integrons (6,8). The qnrS1 gene has been identifi ed either upstream of Tn3-like transposon (9,28) or upstream of the insertion sequence ISEcl2 (17,37). In IncQ-related plasmid pGNB2 and in pMG308 from a Salmonella isolate, surrounding genetic structures of the qnrS2 genes were similar, with 2 open reading frames located immediately downstream of qnrS2, similar to repC and repA genes involved in plasmid replication (24,25) (Figure 2).…”

“…The QnrA determinants have been reported worldwide in many enterobacterial species, and 6 of them are known so far (QnrA1 to QnrA6) (8). Other plasmid-mediated quinolone resistance determinants, QnrB (QnrB1 to QnrB10) and QnrS (QnrS1 and QnrS2), have been identifi ed in enterobacterial species, sharing 41% and 60% amino acid identity with QnrA, respectively (8)(9)(10). The plasmid-mediated qnr genes have been identifi ed so far only in Enterobacteriaceae (6,8).…”

Prevalence of plasmid-mediated quinolone-resistance determinants in Shigella flexneri isolates from Anhui Province, China

“…15,18 Genetic clones were identified according to criteria established by Tenover et al 18 RESULTS AND DISCUSSION PMQR determinants were present in 53.8% (14 of 26) of isolates with qnr, aac(6¢)-Ib-cr and qepA detected alone or in combination (Table 2). qnrA1, qnrS1, qnrS2, aac(6¢)-Ib-cr and qepA were present in 30.8% (8 of 26), 11.5% (3 of 26), 3.8% (1 of 26), 19.2% (5 of 26) and 11.5% (3 of 26) of those isolates, respectively. Five isolates carried two or three types of PMQR determinants.…”

“…19 The qnrS1 gene has B60 and B50% homology to the gene of qnrA and qnrB, respectively. There are 17 amino-acid substitutions between QnrS1 and QnrS2, but only one amino-acid substitution between QnrS1 and QnrS3.…”

Plasmid-Mediated Quinolone Resistance

“…Knowledge of the sequence allowed search for qnrA by PCR, and it was soon discovered in a growing number of organisms, including other K. pneumoniae strains in the United States (22,23), Escherichia coli isolates in Shanghai (24), and Salmonella enterica strains in Hong Kong (25). qnrA was subsequently followed by discovery of plasmid-mediated qnrS (26), qnrB (27), qnrC (28), and qnrD (29). The qnrVC gene from Vibrio cholerae can also be located in a plasmid (30-33) or in transmissible form as part of an integrating conjugative element (34).…”