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

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