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A Plasmid-Borne Shewanella algae Gene, qnrA3, and Its Possible Transfer In Vivo between Kluyvera ascorbata and Klebsiella pneumoniae

ABSTRACT The plasmid-borne quinolone resistance gene qnrA1 is prevalent in multidrug-resistant Enterobacteriaceae. A chromosomally encoded homologue in Shewanella algae, qnrA3, has been described. We isolated two qnrA3-positive strains, one of Klebsiella pneumoniae (He96) and one of Kluyvera ascorbata (Kas96), from the feces of an immunocompromised outpatient. The qnrA3 allele was identical to that of S. algae except for 5 nucleotides and differed from qnrA1 by 29 nucleotides affecting three amino acids. The analysis of the qnrA3 genetic environment showed that qnrA3 was inserted downstream from an ISCR1 element at a recombination crossover site described for other resistance genes, including qnrA1, and immediately upstream from IS26, a situation not described before. IS26 preceded an incomplete class 1 integron which contained, among other genes, aac(6′)-Ib-cr, another transferable quinolone resistance gene, and the β-lactamase gene bla OXA-1/30. The 10-kb fragment encompassing qnrA3 was compared to previously described qnrA1-containing plasmids and multidrug-resistant plasmids; it shares identical sequences with pC15a, pHSH2, pQR1, pQKp311H, and pSAL-1 but with rearrangements, deletions, and mutations. Conjugal transfer of qnrA3 was highly efficient (10−2) from K. pneumoniae He96 or K. ascorbata Kas96 to Escherichia coli J53 but less so (10−5) from either donor to a clinical strain of Enterobacter cloacae. This first description of a plasmid-borne copy and of the in vitro transfer of qnrA3 is taken to illustrate its likely in vivo transfer from S. algae to the Enterobacteriaceae.