Mechanisms of Resistance to Quinolones

Antimicrobial resistance is a worldwide problem. Various pathogenic bacteria can be resistant to one or several antibiotics, resulting in a serious public health problem. Isolation of pathogenic bacteria resistant to multiple last-generation antibiotics from hospital samples have been reported. In that sense, the isolation of pathogenic strains resistant to members of the quinolone family, from clinical samples, is an increasing phenomenon. Quinolones are a group of synthetic broad-spectrum antimicrobials, whose mechanism of action is the inhibition of DNA gyrase and topoisomerase IV, with the consequent DNA breakdown and cell death due to genotoxic damage. Three mechanisms have been determined by which bacteria can be resistant to quinolones: (1) Chromosomal mutations in coding genes (mutations that alter the objectives of the drug). (2) Mutations associated with the reduction of the intracytoplasmic concentration of quinolones. (3) Plasmid-mediated quinolone resistance genes (plasmids that protect cells from the lethal effects of quinolones). In this chapter, we analyze each of them and provide the most current connections and investigations of these processes.