Research of target genes mutation of Escherichia coli mutants selected in the mutant selection window

Objective To investigate the concentration,structure of fluoroquinolones on the target gene mutation of Escherichia colii mutants selected in the mutant selection window(MSW). MethodsThe target genes, gyrA and parC of Escherichia colii mutants selected in the MSW were obtained by PCR method and sequenced by DNA sequencing. The agar dilution method was carried out to determine minimal inhibition concentration (MIC) of Escherichia coli mutants.ResultsAmong 53 mutants selected by five fluoroquinolones, 79% were Ser-83-Leu mutation detected in the quinolone resistant-determining region of the gyrA gene, 19% were Asp-87Asn mutation, 2% was a Gly81-Cys mutation, and no parC mutation was detectable. MIC90 of mutation at position 83 was 2~8 fold larger than that of mutation at position 81 and 1~2 fold larger than that of mutation at position 87. Mutation at position 83 was the most important factor to influence the sensitivity of Escherichia coli. Conclusion DNA gyrase is the primary target of fluoroquinolone against E.coli,mutation at position 83 and 87 is the most frequent.