RESUMO
Although quinolone resistance results mostly from chromosomal mutations in Enterobacteriaceae,it may also be mediated by plasmid-encoded Qnr determinants.Qnr proteins protect DNA from quinolone action and compromise the effect of quinolones,such as nalidixic acid.Qnr proteins including QnrA,QnrB and QnrS,have been identified worldwide with a quite high prevalence among Asian isolates with a frequent association with clavulanic acid-inhibited expanded-spectrum b-lactamases and plasmid-mediated cephalosporinases.The QnrA genes are embedded in complex sul1-type integrons.A close relative and likely progenitor of the QnrA have been found in the water-borne species Shewanella algae.It may help to determine the location of in vivo transfer of the QnrA genes.Further analyses of the role of quinolones,if any,in enhancing this gene transfer may prevent the spreading of the drug resistance and possibly lead to the finding of a novel mechanism of antibiotic resistance.
