Abstract:

Objective    To investigate the effect of the subinhibitory concentration of quinolones on resistance to quinolones in Mycoplasma pneumoniae (MP) and its mechanisms． Methods    To induce resistance to quinolones, the reference strain FH was cultured for several passages with three different quinolones at sub-inhibitory concentrations. DNA was extracted from the FH strain and in vitro drug-induced quinolone-resistant strains． The quinolone resistancedetermining regions(QRDR) of gyrA, gyrB, parC and parE in each strain were amplified with the corresponding primers by PCR and then sequenced. Results    The  FH  strain exhibited resistance or crossresistance to the three quinolones after  induction． In 6 drug-induced quinolone-resistant strains，the strains induced by levofloxacin had a substitute of Met95→Ile in the gyrA gene and a substitute of Asp87→Tyr in the parC gene; and the strains induced by Gatifloxacin had a substitute of Arg→Lys in the gyrB gene. No mis-sense mutation was detected in the parC gene. Conclusion    Longterm use of quinolones at sub-inhibitory concentration can contribute to resistance and cross-resistance of MP． The mutation of QRDR is closely associated with  quinolone-resistance．

Key words: Pneumonia， mycoplasma； Quinolones； Drug resistance, microbial; Point mutation