Induction And Mechanisms Of Resistance To Quinolones In Mycoplasma Pneumoniae

Mycoplasma pneumoniae(Mp) is the etiological agent of respiratory tract infections.In recent years,the percentage of Mycoplasma pneumoniae infection was rising.It was an important pathogen of Community-acquired pneumonia. The macrolides were the preferred drugs in the treatment of mycoplasma pneumoniae infection.But the high rate of drug resistance of the macrolides was observed. Fluoroquinolones offer the potential for empirical treatment.Newer compounds of this class have activity against mycoplasmas that is improved over that of older fluoroquinolones.The intracellular targets of fluoroquinolones were considered to be the type II topoisomerases,DNA gyrase and topoisomerase IV.The quinolone-resistant mycoplasma pneumoniae wae not found currently. However, in human mycoplasma,the quinolone-resistant mycoplasma hominis and ureaplasma urealyticum had been clinically isolated.Through the amplification of quinolone resistance-determining region of gyrA, gyrB, parC, and parE genes,It was confirmed that mycoplasma hominis and ureaplasma urealyticum resistance was relationg to the gyrA and parC point mutations in the genes. This study was planned to based on the theory of pressure of drug causing bacteria resistance, in the way of manual inducement, passage a susceptible strain of mycoplasma pneumoniae onto Ciprofloxacin,Levofloxacin or Gatifloxacin containing culture medium to obtain resistant mutants step by step in the laboratory.Through measuring the mininmum inhibition concentration(MIC) of Ciprofloxacin,Levofloxacin and Gatifloxacin,we observed the change in resistances.Through amplifing the quinolone resistance-determining regions of gyrA, gyrB, parC, and parE genes,we could know the relationship between resistances and point mutations in the genes. This study could provide a theoretical basis and countermeasures for the prevention and treatment of mycoplasma pneumoniae infection.Objective To investigate the effects and mechanisms of the subinhibitory concentration of quinolones on resistance to quinolones in Mycoplasma pneumoniae.Methods To induce resistance to quinolones, the reference strain FH were cultured for several passages with three difierent quinolones at subinhibitory concentrations.The drug-induced quinolone-resistant strains were measured the minimal inhibitory concentration.DNA was extracted from the strain FH, and in vitro drug-induced quinolone-resistant strains. The quinolone resistance-determining regions (QRDR) of gyrA,gyrB,parC and parE of each strain were amplified with the corresponding primers by PCR and then sequenced.Results The strain FH exhibited resistance or cross-resistance to the three quinolones after the 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 substitude of Asp87→Tyr in the parC gene;and the strains induced by Gatifloxacin had a substitute of Arg→Lys in the gyrB gene.No missense mutation was detected in the parC gene.Conclusion Long-term use of quinolones at subinhibitory concentration can contribute to resistance and cross-resistance of MP. The mutation of QRDR is closely associated to the quinolone resistance.