Erythromycin Resistance in Streptococcus pyogenes and Macrolide Consumption in a Central Italian Region

Background: The study investigated macrolide resistance in Streptococcus pyogenes in a central Italian area from 2001 to 2006 and the possible correlation between antibiotic consumption and fluctuations of resistance percentages. Materials and Methods: Macrolide and lincosamide susceptibility of 1,419 S. pyogenes isolates was tested by Kirby Bauer method. Macrolide consumption was valuated as defined daily dose/1,000 inhabitants per day (DID), according to the World Health Organization anatomic therapeutic chemical classification. Spearman's correlation coefficient was used to assess the association between resistance and use of (1) all macrolides pooled, (2) once daily, (3) twice daily, and (4) three times daily dosage regimens. Results: In total, 320 strains (22.6%) were erythromycin-resistant, 11.4% with the M phenotype and 11.2% with the MLS phenotype. There was a significant decrease in erythromycin resistance during the study period-from 28.1% in 2001 to 15.6% in 2006 (p < 0.01). No significant correlation was found between erythromycin resistance and local overall macrolide consumption, neither during the same year nor during the previous year. In contrast, a significant correlation was found between resistance rates and once-daily macrolide use during the preceding 6 months in Siena r = 0.747, p = 0.008). Conclusion: The known greater selective effect of long-acting agents could establish a pressure outcome, resulting in a specific local epidemiology during a relatively short time gap.