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Macrolide-resistance genes in clinical isolates of Streptococcus pyogenes
Carmela Cascone1, Maria Santagati, Silvana Noviello
1Department of Microbiological Sciences, University of Catania, Italy.
Abstract:
Macrolide-resistance genes were investigated in 103 macrolide-resistant strains of Streptococcus pyogenes, isolated from children with pharyngotonsillitis. The presence of mef(A), erm(B), and erm(TR) genes was detected by PCR. mef(A) was found in 48 out of 103 (46.6%) strains, whereas erm(B) was detected in 43 isolates (41.7%). All mef(A) strains showed a typical M phenotype (resistance to 14- and 15-membered macrolides, and sensitivity to lincosamides and streptogramin B), whereas erm(B) strains had the MLSB phenotype (resistance to macrolides, lincosamides, and streptogramin B antibiotics). erm(TR) was found in 10 strains, always together with other resistance genes. In seven cases erm(TR) was associated with erm(B), and three cases with mef(A). In two isolates with the M phenotype (1.9%), it was not possible to detect the presence of any of the three macrolide resistance genes tested. Inducible resistance to macrolides was shown for 24 out of the 53 MLSB strains. Analysis of macrorestriction fragment patterns by pulsed-field gel electrophoresis showed that erythromycin-resistant S. pyogenes are polyclonal, however each phenotype, MLSB and M, formed essentially homogeneous groups.
Insights
Macrolide resistance in Streptococcus pyogenes is often due to mef(A) or erm(B) genes, leading to distinct resistance phenotypes. These macrolide-resistant strains are polyclonal but form homogeneous groups based on their resistance patterns.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Streptococcus pyogenes is a common cause of pharyngotonsillitis in children.
- Macrolide antibiotics are frequently used to treat S. pyogenes infections.
- The emergence of macrolide resistance in S. pyogenes poses a significant public health concern.
Purpose of the Study:
- To investigate the prevalence and types of macrolide-resistance genes in S. pyogenes strains isolated from children with pharyngotonsillitis.
- To correlate the presence of specific resistance genes with observed macrolide resistance phenotypes.
- To analyze the genetic relatedness of macrolide-resistant S. pyogenes isolates.
Main Methods:
- Polymerase Chain Reaction (PCR) was used to detect macrolide-resistance genes (mef(A), erm(B), erm(TR)).
- Macrolide resistance phenotypes (M and MLSB) were determined.
- Pulsed-field gel electrophoresis (PFGE) was employed for macrorestriction fragment pattern analysis.
Main Results:
- The mef(A) gene was detected in 46.6% of strains, associated with the M phenotype.
- The erm(B) gene was found in 41.7% of strains, associated with the MLSB phenotype.
- erm(TR) was present in 10 strains, often co-occurring with mef(A) or erm(B).
- Inducible macrolide resistance was observed in 24/53 MLSB strains.
- PFGE analysis indicated that erythromycin-resistant S. pyogenes strains are polyclonal but form distinct phenotypic groups.
Conclusions:
- Macrolide resistance in S. pyogenes is primarily mediated by mef(A) and erm(B) genes, conferring distinct resistance profiles.
- The genetic diversity of resistant strains suggests multiple origins or acquisition events.
- Understanding these resistance mechanisms and genetic patterns is crucial for effective antibiotic treatment strategies.