DETECTION OF MUTATIONS IN PARC IN QUINOLONE-RESISTANT CLINICAL ISOLATES OF ESCHERICHIA-COLI

The gene parC encodes the A subunit of topoisomerase IV of Escherichia coli. Mutations in the parC region analogous to those in the quinolon e resistance-determining region of gyrA were investigated in 27 clinic al isolates of E. coli for which ciprofloxacin MICs were 0.007 to 128 mu g/ml. Of 15 isolates for which ciprofloxacin MICs were greater than or equal to 1 mu g/ml, 8 showed a change in the serine residue at pos ition 80 (Ser-80), 4 showed a change in Glu-84, and 3 showed changes i n both amino acids. No mutations were detected in 12 clinical isolates for which ciprofloxacin MICs were less than or equal to 0.25 mu g/ml. These findings suggest that ParC from E. coli may be another target f or quinolones and that mutations at residues Ser-80 and Glu-84 may con tribute to decreased fluoroquinolone susceptibility.