qnr Gene Nomenclature

Abstract

6Since the plasmid-borne quinolone resistance gene qnr was reported in 1998 (8), many additional qnr alleles have been discovered on plasmids or the bacterial chromosome (reviewed in references 9 and 13). The plasmid-borne qnr genes currently comprise three families, qnrA, qnrB, and qnrS, differing from each other 40% or more in nucleotide sequence. Within each family, minor (Յ10%) variation in sequence has defined a growing number of alleles. For the qnrA and qnrS families, the number of variants has been manageable, with general agreement on allele designations, but lately, the number of qnrB sequences submitted to GenBank has exploded, with the same qnrB allele number claimed for dissimilar sequences by different investigators and the same entry given new allele numbers from week to week.To bring order into the current qnrB numbering chaos, we propose numbering the qnr alleles according to the following rules: (i) priority should be given first to published numbers, then to those in accepted or submitted manuscripts, and finally to the date of submission to GenBank; (ii) only full-length sequences should be assigned allele numbers; (iii) naturally occurring alleles, not those created by mutation, will be numbered; (iv) only nucleotide alterations that result in amino acid changes and not functionally silent substitutions should be taken into account; (v) one or more amino acid alterations define a new allele; (vi) variation in promoter sequences is not considered; (vii) demonstration that an allele in an established family causes reduced susceptibility to nalidixic acid or a fluoroquinolone is desirable but is not required; (viii) a new family (such as qnrC) should differ substantially from existing families (Ն30% difference suggested in nucleotides or derived amino acids) and should be shown to affect quinolone susceptibility; (ix) a database of qnr allele designations will be maintained at http://www.lahey.org/qnrStudies; and (x) further allele numbers will be assigned upon application.Another source of confusion is the presence of two potential in-frame initiation codons for some qnrB alleles. For other qnrB alleles, the first ATG is out of phase with the second. The

Sm qnr , a New Chromosome-Carried Quinolone Resistance Gene in Stenotrophomonas maltophilia

“…QnrA1 confers resistance to quinolones and increases the MICs of fluoroquinolones up to 32-fold (8). Since then, several proteins belonging to the Qnr family have been described in members of the family Enterobacteriaceae (6). The source of the plasmid-mediated qnrA genes has been identified in the chromosome of Shewanella algae (9), while the possible source of the plasmid-mediated qnrS determinants was identified in the chromosome of Vibrio splendidus (3).…”

Prevalence of Plasmid-Mediated Quinolone Resistance Genes and Ciprofloxacin Resistance in Pediatric Bloodstream Isolates of Enterobacteriaceae over a 9-Year Period

“…Mutations in the quinolone resistance-determining region (QRDR) and the presence of plasmidmediated quinolone resistance (PMQR) genes contribute to quinolone resistance in complex and diverse ways (1)(2)(3). However, only limited studies have addressed the quinolone resistance of Enterobacteriaceae in pediatric isolates so far; long-term studies involving bloodstream isolates are even fewer in number (4)(5)(6).…”

“…PMQR genes were first described in a clinical isolate of K. pneumoniae in 1998 (14). Since then, 5 groups of qnr determinants, qnrA, qnrB, qnrC, qnrD variant, and qnrS, have been identified (2). Three additional PMQR genes have also been described; aac(6?…”

Mutant prevention concentrations of ciprofloxacin against urinary isolates of Escherichia coli and Klebsiella pneumoniae

“…The transferable qnr determinants were identified in Gram negative clinical isolate plasmid; these genes encode for a pentapeptide repeat protein that binds to and protects type II DNA topoisomerases from inhibition by quinolones [4]. Five types of qnr genes have been reported: qnrA, qnrB, qnrS, qnrC, and qnrD, and some of them have several allelic variants [5,6]. In addition to the qnr genes, several new mechanisms of plasmid-mediated quinolone resistance (PMQR) genes have been discovered during the past decade, including the aac(6')-Ib-cr and qepA genes [7].…”