Analysis of mutations to gyrA in quinolone-resistant clinical isolates of Enterobacter cloacae

The gyrA subgenes of a quinolone-resistant Enterobacter cloacae clinical isolate (ofloxacin MIC, 16 mg/L) and of a control, E. cloacae NCTC 10005 (ofloxacin MIC, 0.03 mg/L), were amplified by polymerase chain reaction (PCR) and sequenced. The resistant isolate had mutations at the codons for amino acids 83, 89 and 90, The first of these mutations led to replacement of serine-83 by tyrosine, whereas the other mutations were silent, Digestion of PCR-amplified DNA fragments with the restriction enzyme HinfI detected mutations at the same site in gyrA in six further quinolone resistant E, cloacae isolates.