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Susceptibility of Streptococcus pyogenes to azithromycin, clarithromycin, erythromycin and roxithromycin in vitro

G J Van Asselt1, J H Sloos, R P Mouton

  • 1Department of Medical Microbiology, University Hospital Leiden, The Netherlands.

Journal of Medical Microbiology
|November 1, 1995
PubMed

Insights

Streptococcus pyogenes remains highly susceptible to macrolide antibiotics like azithromycin and erythromycin. Resistance is rare, with only 0.5% of strains showing inducible macrolide-lincosamide-streptogramin B resistance.

Area of Science:

  • Microbiology
  • Infectious Diseases
  • Pharmacology

Background:

  • Streptococcus pyogenes (group A streptococci) is a significant human pathogen.
  • Macrolide antibiotics are crucial for treating S. pyogenes infections.
  • Understanding macrolide susceptibility is vital for effective treatment strategies.

Purpose of the Study:

  • To assess the in vitro susceptibility of clinical S. pyogenes isolates to four macrolide antibiotics.
  • To compare the accuracy of three different antimicrobial susceptibility testing methods.
  • To determine the prevalence of macrolide resistance in Dutch S. pyogenes isolates.

Main Methods:

  • Testing 180 and 436 clinical S. pyogenes isolates against azithromycin, clarithromycin, erythromycin, and roxithromycin.
  • Utilizing microbroth MIC, E-test, and disk diffusion assays to determine Minimum Inhibitory Concentrations (MICs) and Minimum Bactericidal Concentrations (MBCs).
  • Investigating the resistance mechanisms in erythromycin-resistant strains.

Main Results:

  • All tested macrolides demonstrated potent in vitro activity against S. pyogenes, with MIC90 values ≤ 0.5 mg/L.
  • Erythromycin exhibited the lowest MIC90 (0.09 mg/L), suggesting slightly higher activity compared to other macrolides.
  • Minimal discrepancies were found between the three susceptibility testing methods.
  • Macrolide resistance was very low (0.5%), with resistant strains displaying inducible macrolide-lincosamide-streptogramin B resistance.

Conclusions:

  • Clinical isolates of Streptococcus pyogenes in The Netherlands remain highly susceptible to commonly used macrolide antibiotics.
  • The macrolide antibiotics azithromycin, clarithromycin, erythromycin, and roxithromycin are effective against S. pyogenes in vitro.
  • Inducible macrolide-lincosamide-streptogramin B resistance is the primary mechanism observed in the few resistant strains.

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