Objective: To investigate the relationship between different fluoroquinolone (FQ) resistance of Streptococcus pneumoniae and the mutations of target genes.
Methods: A total of 232 Streptococcus pneumoniae isolates were collected from 12 teaching hospitals at 9 cities between June and December 2010. The antibacterial activities of 16 antimicrobial agents were determined by agar dilution method. The ciprofloxacin, levofloxacin and moxifloxacin MIC ≥ 1 mg/L isolates were selected to detect the mutations in QRDR (parC, parE, and gyrA genes) through PCR combined sequencing.
Results: The susceptible rates of ciprofloxacin, levofloxacin and moxifloxacin were 53.9% (125/232) , 98.7% (229/232) , 98.7% (229/232) .Forty-three strains were randomly selected to be analyzed, including 19 levofloxacin MIC ≥ 2 mg/L strains and 24 levofloxacin MIC = 1 mg/L strains. The MIC of levofloxacin were 1-2 mg/L, ciprofloxacin were 2 mg/L and moxifloxacin were 0.125-0.250 mg/L when a single mutation in parE occurred. The MIC of levofloxacin were 2 mg/L, ciprofloxacin were 4 mg/L and moxifloxacin were 0.25 mg/L or 0.50 mg/L when mutations in both parE and parC occurred. The MIC of levofloxacin were 16 mg/L, ciprofloxacin were ≥ 16 mg/L and moxifloxacin were 4 mg/L when mutations in both parE and gyrA occurred.
Conclusion: The single mutation in parE/parC is associated with low level levofloxacin and ciprofloxacin resistance, while double mutations in both parC/parE and gyrA are associated with moxifloxacin resistance.