CHARACTERIZATION OF MYCOPLASMA-HOMINIS MUTATIONS INVOLVED IN RESISTANCE TO FLUOROQUINOLONES

Fluoroquinolone-resistant mutants of Mycoplasma haminis were selected in vitro from the PG21 susceptible reference strain either by multiste p selection on increasing concentrations of various fluoroquinolones o r by one-step selection on agar medium with ofloxacin. The quinolone r esistance-determining regions (QRDR) of the structural genes encoding the A and B subunits of DNA gyrase were amplified by PCR, and the nucl eotide sequences of eight multistep-selected resistant strains were co mpared to those of susceptible strain PG21. Four high-level resistant mutants that were selected on norfloxacin or ofloxacin contained a C-t o-T transition in the gyrA QRDR, leading to substitution of Ser-83 by Leu in the GyrA protein. Analysis of the sequence of the gyrB QRDR of the eight multistep-selected mutants did not reveal any difference com pared to that of the gyrB QRDR of the reference strain M. hominis PG21 . Similar analyses of eight one-step-selected mutants did not reveal a ny base change in the gyrA and gyrB QRDRs. These results suggest that in M. hominis, like in other bacterial species, a gyrA mutation at Ser -83 is associated with fluoroquinolone resistance.