Clinical Microbiology and Antimicrobial Chemotherapy. 2012; 14(2):153-161
Here we report on a high incidence of quinolone resistance (43,1%) among nosocomial CTX-M-5 ESBLproducing S. Typhimurium isolates belonging to a single clonal group isolated in Russia, Belarus, and Kazakhstan. The resistance mechanism in all cases was a single point mutation in quinolone resistance-determining region (QRDR) of DNA-gyrase subunit A (GyrA), however the discovered amino acid substitutions at GyrA positions 83 or 87 were different. The high incidence of quinolone resistance and the apparent diversity of GyrA mutations are likely explained by increased mutation rate (hypermutability) observed in all isolates of the described clonal group.