Prevalence of pneumococci with single mutations within fluoroquinolone resistance genes

Background: Discordant antibiotic treatment of fluoroquinolone (FQ) resistant pneumococci causes treatment failure in patients with pneumonia. Resistance to FQs occurs in a stepwise fashion by the acquisition of mutations within the FQ binding sites (QRDR) in the target enzymes DNA gyrase (gyrA and gyrB), and topoisomerase IV (parC and parE). Whereas complete resistance to FQs mainly occurs if mutations in both target enzymes are present, strains containing single mutations in only one of the enzymes frequently have susceptible phenotypes and cannot be detected by microbiological routine testing. These first-ste…