Fluoroquinolone (FQ) resistance is usually caused by point mutations within the quinolone resistance-determining regions (QRDRs) of gyrA, gyrB, parC and/or parE. However, little is known about the worldwide increase in FQ-resistant Escherichia coli or, more specifically, about the geographical distribution of QRDR mutations and the clonal spread of isolates. In this study, we analysed 68 FQ-resistant E. coli isolates from eight Asian countries using QRDR amino acid mutation patterns and examined their susceptibility to FQs. Of the isolates, 38% had mutations at S83 and D87 of GyrA and S80 of ParC (MM/-/M-/-) and 34% had mutations at S83 and D87 of GyrA, S80 of ParC and S458 of ParE (MM/-/M-/M). MIC50 values (minimum inhibitory concentrations for 50% of the isolates) for isolates with at least mutation at S458 of ParE for ciprofloxacin and prulifloxacin were relatively higher than MIC50 values of isolates without this mutation. Based on their geographic distribution and the QRDR mutation patterns, the isolates were divided into a common type in which the organisms were isolated from three or more countries, and a local type in which the isolates were from one or two countries. Mutation types at S83L and D87N in GyrA and S80I in ParC with no or another site in the QRDR were the most frequent among the FQ-resistant isolates, especially among the common type. Gene typing indicated that isolates in the common type were not similar between countries. These data suggest that the increase in FQ-resistant E. coli strains is mainly generated by mutations in the QRDR in each geographical area rather than through intercontinental spread.
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