Mechanisms involved in quinolone resistance in Mycoplasma mycoides subsp. capri

• Norfloxacin selected mutants differ from enrofloxacin and ciprofloxacin mutants.
• QRDR mutations, especially in GyrA and ParC, account for fluoroquinolone resistance.
• There is evidence of an ATP dependent efflux system.

Mycoplasma mycoides subsp. capri is a causative agent of contagious agalactia in goats. In this study, M. mycoides subsp. capri mutants were selected for resistance to fluoroquinolones (norfloxacin, enrofloxacin and ciprofloxacin) by serial passes in broth with increasing concentrations of antibiotic. Mutations conferring cross-resistance to the three fluoroquinolones were found in the quinolone resistance determining regions of the four genes encoding DNA gyrase and topoisomerase IV. Different mutations in the DNA gyrase GyrA subunit suggest a different mechanism of inhibition between norfloxacin and the other tested fluoroquinolones. The presence of an adenosine triphosphate-dependent efflux system was suggested through the use of the inhibitor orthovanadate.