In vitro selection of resistance to clarithromycin in Streptococcus pneumoniae clinical isolates

L. Drago, E. De Vecchi, L. Nicola, D. Legnani, M. Prenna, S. Ripa

Research output: Contribution to journalArticlepeer-review


In this study the effects of exposure to serum, lung and breakpoint concentrations on Streptococcus pneumoniae susceptibility to clarithromycin, azithromycin, amoxicillin/clavulanate, levofloxacin and moxifloxacin were evaluated. Development of resistance was determined by multi-step and single-step methodologies. In the first experimental set, minimum inhibitory concentrations (MICs) were determined after 10 passages on antibiotic-gradient plates and 10 passages on antibiotic-free plates. Acquisition of resistance was defined as an increase of ≥4-fold from the starting MIC. In single-step studies, the rate of spontaneous mutations was calculated after a passage on antibiotic-containing agar plates. Azithromycin and levofloxacin gave the highest number of strains with MIC increased of at least 4 times the starting value, followed by moxifloxacin and by clarithromycin which only at the lowest concentration tested selected for resistance in 5 strains. Amoxicillin/ clavulanate never displayed ≥4-fold MIC increase. Frequencies of mutation were lower for clarithromycin and moxifloxacin than for the comparators. At lung concentrations clarithromycin had limited potential to select for resistance.

Original languageEnglish
Pages (from-to)161-168
Number of pages8
JournalJournal of Chemotherapy
Issue number2
Publication statusPublished - Apr 2005


  • Amoxicillin/ clavulanate
  • Azithromycin
  • Clarithromycin
  • Levofloxacin
  • Moxifloxacin
  • Resistance
  • Streptococcus pneumoniae

ASJC Scopus subject areas

  • Pharmacology (medical)
  • Microbiology (medical)


Dive into the research topics of 'In vitro selection of resistance to clarithromycin in Streptococcus pneumoniae clinical isolates'. Together they form a unique fingerprint.

Cite this