In vitro selection of resistance in Streptococcus pneumoniae at in vivo fluoroquinolone concentrations

E. De Vecchi, L. Nicola, F. Ossola, Lorenzo Drago

Research output: Contribution to journalArticlepeer-review


Objectives: To compare the ability to select for resistance in Streptococcus pneumoniae of levofloxacin, moxifloxacin, ciprofloxacin and prulifloxacin. Methods: Twenty strains of S. pneumoniae susceptible to fluoroquinolones were used. The frequencies of spontaneous single-step mutations at plasma and epithelial lining fluid (ELF) peak and trough antibiotic concentrations were calculated. Multi-step selection of resistance was evaluated by performing 10 serial subcultures on agar plates containing a linear gradient from peak to trough antimicrobial concentrations, followed by 10 subcultures on antibiotic-free agar. Resistant strains selected after multi-step selection were characterized for DNA mutations by sequencing gyrA, gyrB, parC and parE genes. Results: Levofloxacin and moxifloxacin showed the lowest frequencies of mutations (median -11) at plasma peak and at ELF concentrations, while medians ranging from 10-8 to 10-6 were observed for ciprofloxacin and prulifloxacin. In a multi-step selection assay, ciprofloxacin and prulifloxacin selected for the highest number of resistant strains (19 and 31, respectively). No selection of resistance was observed for levofloxacin at ELF concentrations and for moxifloxacin at plasma and ELF concentrations. Mutations in parC, parE and gyrA genes were found in ciprofloxacin- and prulifloxacin-resistant strains, while only parC mutations were found for levofloxacin. Conclusions: Levofloxacin and moxifloxacin are characterized by a lower propensity to select in vitro for resistance in S. pneumoniae than ciprofloxacin and prulifloxacin, when tested at plasma and lung concentrations.

Original languageEnglish
Pages (from-to)721-727
Number of pages7
JournalJournal of Antimicrobial Chemotherapy
Issue number4
Publication statusPublished - 2009


  • Ciprofloxacin
  • Frequency of mutation
  • Levofloxacin
  • Moxifloxacin
  • Prulifloxacin

ASJC Scopus subject areas

  • Infectious Diseases
  • Pharmacology (medical)
  • Pharmacology


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