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Declining macrolide resistance in Streptococcus pyogenes in Portugal (2007-13) was accompanied by continuous clonal
C Silva-Costa1, M Ramirez2, J Melo-Cristino1
1Instituto de Microbiologia, Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal.
Objectives:
Macrolide resistance among Streptococcus pyogenes [group A streptococci (GAS)] in Portugal decreased between 1999 and 2006 and this decrease was accompanied by alterations in the prevalence of macrolide resistance phenotypes and clonal composition of the population. The aims of this study were to determine the macrolide resistance rate, resistance phenotypes and clones of GAS recovered from pharyngitis in 2007-13 in Portugal.
Methods:
Antimicrobial susceptibility was tested by disc diffusion. Macrolide-resistant isolates were characterized by emm typing, T typing, PFGE profiling and MLST, and the presence of macrolide resistance determinants was determined by PCR.
Results:
We found continuing changes in macrolide resistance phenotypes and a persistent decline in overall erythromycin resistance, from 10% in 2007 to 1% in 2013. During this period there was a marked increase in emm11-ST403 cMLSB isolates, the disappearance of the emm3-ST315 M lineage and changes in the prevalence of previously identified GAS clones. Unexpectedly, the decline in erythromycin resistance and the decreasing prevalence of the MLSB phenotype were accompanied by a high consumption of long-acting and intermediate-acting macrolides, known to select for resistance and particularly for the erm(B) gene.
Conclusions:
The continuous decline in macrolide resistance detected since 2000, accompanied by a high clonal instability, emphasizes the importance of considering factors other than antibiotic consumption in explaining the prevalence of macrolide-resistant GAS.
Insights
Group A Streptococcus (GAS) macrolide resistance in Portugal declined significantly from 2007-2013, with evolving resistance phenotypes and clones. This trend persisted despite high macrolide use, suggesting factors beyond antibiotic consumption influence resistance.
Area of Science:
- Microbiology
- Infectious Diseases
- Epidemiology
Background:
- Macrolide resistance in Streptococcus pyogenes (group A streptococci, GAS) in Portugal showed a decrease between 1999 and 2006.
- This decrease was linked to shifts in resistance phenotypes and the population's clonal makeup.
Purpose of the Study:
- To ascertain the macrolide resistance rate, phenotypes, and GAS clones from pharyngitis cases in Portugal between 2007 and 2013.
- To monitor trends in macrolide resistance following the previously observed decline.
Main Methods:
- Antimicrobial susceptibility testing using disc diffusion.
- Characterization of macrolide-resistant isolates via emm typing, T typing, PFGE profiling, and MLST.
- Detection of macrolide resistance determinants using PCR.
Main Results:
- Erythromycin resistance in GAS persistently declined from 10% in 2007 to 1% in 2013.
- A notable increase in emm11-ST403 cMLSB isolates was observed, alongside the decline of the emm3-ST315 M lineage.
- Despite high macrolide consumption, erythromycin resistance and MLSB phenotype prevalence decreased, with the erm(B) gene being particularly selected.
Conclusions:
- The ongoing reduction in macrolide resistance in GAS since 2000 continues.
- High clonal instability in GAS populations is evident.
- Factors beyond antibiotic consumption are crucial for understanding macrolide-resistant GAS prevalence.
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