Genetic commonality of macrolide-resistant group A beta hemolytic streptococcus pharyngeal strains

Ann Clin Microbiol Antimicrob. 2009 Dec 1;8:33. doi: 10.1186/1476-0711-8-33.


Background: Group A beta hemolytic streptococcus (GABHS) pharyngitis is a common childhood illness. Penicillin remains the gold standard therapy, but macrolides are indicated for the penicillin allergic patient, and are often used for convenience.

Methods: We conducted a surveillance study of children with pharyngitis and positive streptococcal rapid antigen testing from 10/05 to 10/06 at 2 sites (A & B). Demographics, treatment, and resistance data was collected and compared to previous data from 2002. Erythromycin (EM) resistance was determined by disk diffusion and E-test on 500 isolates. Pulse field gel electrophoresis (PFGE) was performed to measure genetic relatedness of isolates. StatXact version 8 software (Cytel Inc., Cambridge, MA) was utilized to perform Fisher's exact test and exact confidence interval (CI) analysis.

Results: There were no differences in resistance rates or demographic features, with the exception of race, between sites A & B. EM resistance was 0 in 2002, 3.5% in 2005-06 at site A, and 4.5% in 2005-06 at site B. 3/7 and 3/9 had inducible resistance at A and B respectively. 8 isolates had relatedness > or =80%, 5 of which were 88% homologous on PFGE.

Conclusion: Community macrolide resistance has increased following increased macrolide use. These results may have treatment implications if use continues to be high.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Bacterial Proteins / genetics
  • Child
  • Drug Resistance, Multiple, Bacterial*
  • Female
  • Humans
  • Macrolides / pharmacology*
  • Male
  • Microbial Sensitivity Tests
  • Pharyngitis / microbiology*
  • Prospective Studies
  • Streptococcal Infections / microbiology*
  • Streptococcus pyogenes / drug effects
  • Streptococcus pyogenes / genetics*


  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Macrolides