Origin of plasmid-mediated quinolone resistance determinant QnrA

Abstract

Plasmid-mediated resistance to quinolones is increasingly reported in studies of Enterobacteriaceae. Using a PCR-based strategy, a series of gram-negative species were screened for qnrA-like genes. Shewanella algae, an environmental species from marine and fresh water, was identified as its reservoir. This is a one of the very few examples of progenitor identification of an acquired antibiotic resistance gene.

FIG. 1.

(Panel 1) Pulsed-field gel electrophoresis profiles of I-Ceu-I digested whole-cell DNAs of Shewanella sp. strains. Lane A, S. putrefaciens reference strain CIP8040 (Institut Pasteur, Paris); lane B, S. algae clinical isolate KB-1; lane C, S. algae reference strain CIP106454T. (Panels 2 and 3) Southern hybridization was performed with a specific probe for the 16S-23S rRNA gene (6) and an internal probe for the qnrA gene (15). The horizontal arrow indicates hybridization position with the qnrA probe. Negative hybridization results with the qnrA probe were obtained for the S. putrefaciens reference strain.

FIG. 2.

Sequence comparison of plasmid-mediated QnrA-like determinants to those of S. algae strains. The plasmid-mediated QnrA1 and QnrA2 determinants are from K. pneumoniae from the United States (16) and from Klebsiella oxytoca from China (GenBank accession number AY675584), respectively. QnrA3 is from S. algae reference strain CIP106454T and S. algae clinical isolate KB-1, whereas QnrA4 and QnrA5 are from S. algae clinical isolates KB-2 and KB-3, respectively (10). DQ058661, DQ058662, and DQ058663 are GenBank accession numbers for QnrA3, QnrA4, and QnrA5, respectively. Dashes are for identical amino acid residues. Pentapeptide motifs in which amino acid substitutions have been identified compared to the QnrA1 sequence are boxed. In these motifs, the conserved residues identified by Tran and Jacoby (29) are shaded.