qnrD , a Novel Gene Conferring Transferable Quinolone Resistance in Salmonella enterica Serovar Kentucky and Bovismorbificans Strains of Human Origin

Abstract

In a previous study, four Salmonella isolates from humans in the Henan province of China showed reduced susceptibility to ciprofloxacin (MIC, 0.125 to 0.25 g/ml) but were susceptible to nalidixic acid (MIC, 4 to 8 g/ml). All isolates were negative for known qnr genes (A, B, and S), aac(6)Ib-cr, and mutations in gyrA and parC. Plasmid DNA was extracted from all four isolates and transformed into Escherichia coli TG1 and DH10B cells by electroporation, and transformants were selected on 0.06 g/ml ciprofloxacin containing brain heart infusion agar plates. Resistance to ciprofloxacin could be transferred by electroporation, and a similar 4,270-bp plasmid was found in all transformants. By sequence analysis, the plasmid was found to carry an open reading frame that had similarities to other qnr genes and that encoded a 214-amino-acid pentapeptide repeat protein. This gene, designated qnrD, showed 48% similarity to qnrA1, 61% similarity to qnrB1, and 41% similarity to qnrS1. Further subcloning of the qnrD coding region into the constitutively expressed tetA gene of vector pBR322 showed that the gene conferred an increase in the MIC of ciprofloxacin by a factor of 32 (from an MIC of 0.002 to an MIC of 0.06 g/ml). For comparison, qnrA1 and qnrS1 were also subcloned into pBR322 and transformed into DH10B cells, conferring MICs of 0.125 and 0.5 g/ml, respectively. A phylogenetic analysis of all known qnr sequences was performed and showed that qnrD was more closely related to the qnrB variants but formed an independent cluster. To our knowledge, this is the first description of this qnrD gene.

Detection of the Smqnr quinolone protection gene and its prevalence in clinical isolates of Stenotrophomonas maltophilia in China

“…Rather, overexpression of the multidrug efflux pump SmeDEF can lead to high-level quinolone resistance in S. maltophilia, whilst low-level quinolone resistance is mediated by a qnr determinant encoded on the chromosome (Cavaco et al, 2009;Valdezate et al, 2005).…”

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

“…Screening of qnr, qepA, aac(6¢)-Ib-cr, gyrA, gyrB, parC, parE and bla genes Amplification of qnr, qepA and aac(6¢)-Ib-cr was performed using the methods described previously; 8,9,11,12 different primers (shown in Table 1) were used for the amplification of qnrB and qnrA subtypes in this study. Amplification of bla genes (b-lactamase genes) was also performed with the methods described previously for bla TEM , bla SHV and bla CTXÀM .…”

Antibiotic resistance and resistance genes in Escherichia coli from poultry farms, southwest Nigeria

“…and tet(39) in tetracycline resistant isolates, cmlA, catA1 and floR (primers for floR: Flor-1, 5'-ATGGCAGGCGATATTCATTA-3'; flor-2: 5'-AAACGGGTTGTCACGATCAT-3') in chloramphenicol resistant isolates, acc(3)-IV in gentamicin resistant isolates, qnrA, qnrB, qnrC, qnrD, qnrS, aac(6')Ib and qepA in isolates resistant to ciprofloxacin (≥ 0.125mg/L) but sensitive to nalidxic acid with MIC ≤ 32 mg/L [20,[22][23][24][25]. The variable regions of Class 1 and Class 2 integrons were amplified and representatives of the different sized amplicons sequenced to characterise their gene contents as described by Peirano et al [21].…”