SmaI macrorestriction analysis of Italian isolates of erythromycin-resistant Streptococcus pyogenes and correlations with macrolide-resistance phenotypes

Microb Drug Resist. Spring 2001;7(1):65-71. doi: 10.1089/107662901750152828.


High rates of erythromycin resistance among Streptococcus pyogenes strains have been reported in Italy in the last few years. In this study, 370 erythromycin-resistant (MIC, > or = 1 microg/mL) Italian isolates of this species obtained in 1997-1998 from throat swabs from symptomatic patients were typed by analyzing SmaI macrorestriction fragment patterns by pulsed-field gel electrophoresis (PFGE). Among the typable isolates (n = 341; the genomic DNA of the remaining 29 isolates was not restricted by SmaI), 48 distinct PFGE types were recognized, of which 31 were recorded in only one isolate (one-strain types). Fifty-two percent of typable isolates fell into three type clusters and 75% into six, suggesting that erythromycin-resistant group A streptococci circulating in Italy are polyclonal, but the majority of them probably derives from the spread of a limited number of clones. In parallel experiments, the 370 test strains were characterized for the macrolide resistance phenotype: 80 were assigned to phenotype cMLS, 89 to phenotype iMLS-A, 33 to phenotype iMLS-B, 11 to phenotype iMLS-C, and 157 to phenotype M. There was a close correlation between these phenotypic data and the genotypic results of PFGE analysis, the vast majority of the isolates assigned to individual PFGE classes belonging usually to a single phenotype of macrolide resistance. All of the 29 untypable isolates belonged to the M phenotype. Further correlations were observed with tetracycline resistance.

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Deoxyribonucleases, Type II Site-Specific / genetics*
  • Electrophoresis, Gel, Pulsed-Field
  • Erythromycin / pharmacology*
  • Humans
  • Italy
  • Microbial Sensitivity Tests
  • Phenotype
  • Restriction Mapping
  • Streptococcal Infections / epidemiology
  • Streptococcal Infections / microbiology*
  • Streptococcus pyogenes / drug effects*
  • Tetracycline Resistance


  • Anti-Bacterial Agents
  • Erythromycin
  • CCCGGG-specific type II deoxyribonucleases
  • Deoxyribonucleases, Type II Site-Specific