qnr Gene Nomenclature

Since 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 (≤10%) 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.