Activity of iclaprim against Legionella pneumophila.

larities. A comparison between the TPqnrS-1a-associated QnrS1 protein and the 218-amino-acid proteins from Vibrio splendidus (accession no. EAP95542) and Vibrio spp. (accession no. EAQ55748)—the latter two considered as a natural reservoir of qnrS genes—revealed 83% and 82% amino acid identity, respectively, and 91% amino acid similarity. Previous studies revealed that the qnrS1 gene is often located on large plasmids that carry additional resistance genes. – 3,6 Although plasmids pAH0376 from S. flexneri and pINF5 from Salmonella Infantis carried a complete Tn3 with a blaTEM-1 b-lactamase gene, recently discovered plasmids of E. cloacae identified the qnrS1 gene in close proximity to the novel b-lactamase gene blaLAP-1. 3 In the present study, we characterized a comparatively small plasmid that carried the qnrS1 gene as the sole resistance gene. To the best of our knowledge, plasmid TPqnrS-1a is the first qnrS1-carrying plasmid for which the complete sequence is available. A detailed sequence analysis of this plasmid suggested that it has most likely derived from an interplasmid recombination event between a qnrS1-carrying plasmid such as pINF5 from Salmonella Infantis or pS5-1 from E. cloacae and a small mobilizable plasmid similar to pEC278 from E. coli. The identification of qnrS1 genes on structurally diverse plasmids points towards the dissemination of these genes and their adaptation in new hosts as relevant factors in the emergence of transferable quinolone resistance.