Abstract: Objective To investigate the effects and mechanisms of the subinhibitory concentration of quinolones on cross-resistance to quinolones in Ureaplasma urealyticum (Uu).Methods To induce resistance to quinolones,three quinolone-sensitive clinical isolates of Uu and the reference strain Uu3 were cultured for 10 to 12 passages with four different quinolones at subinhibitory concentrations (1/2 MIC).DNA was extracted from the strain Uu3,quinolone-resistant clinical isolates,and the in vitro drug-induced quinolone-resistant strains.The quinolone resistance-determining regions (QRDR) of gyrA and parC of each strain were amplified with the corresponding primers by PCR and then sequenced.Results All the quinolone-sensitive clinical isolates and the strain Uu3 exhibited resistance or cross-resistance to the four quinolones after the induction.In 9 quinolone-resistant clinical isolates of Uu and 16 drug-induced quinolone-resistant strains,no missense mutation was detected in the parC gene,whereas 2 missense mutations were detected in the gyrA gene,i.e.V175A (n=8) and N165D (n=1).Conclusion The results suggest that mutations of the gyrA gene may account for the induction of cross-resistance to quinolones in some Uu strains.

Key words: Ureaplasma urealyticum, Quinolones, Drug resistance, microbial, Point mutation