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Molecular typing of erythromycin-resistant streptococcus pyogenes strains with the M phenotype isolated in Italy
S Valisena1, C Falci, A Mazzariol
1Institute of Microbiology, University of Verona, Italy.
Abstract:
To assess the spread of the new M phenotype, various erythromycin-resistant Streptococcus pyogenes strains from three Italian cities (Verona, Monza, Florence) were characterised. Each strain was analysed for the presence of genes ermAM and mefA, for the ability to accumulate radioactive erythromycin in the absence of sodium arsenate, for the protein T serological type, and for the DNA macrorestriction profile identified by means of pulsed-field gel electrophoresis. In a number of strains, the presence of the inducible ermAM gene was demonstrated; all these strains were negative in the efflux-pump detection assay, did not possess the mefA gene, and had similar restriction profiles. The strains with the efflux mechanism and mefA gene belonged to different serotypes. Of these, only one serotype, T4, was isolated in all three cities. The restriction profile analysis with SmaI and SfiI revealed a very close correlation between strains with the same serotype.
Insights
The M phenotype in erythromycin-resistant Streptococcus pyogenes strains is spreading in Italy. Researchers identified the ermAM gene in some strains, while others showed efflux mechanisms and the mefA gene.
Area of Science:
- Microbiology
- Molecular Biology
- Epidemiology
Background:
- Erythromycin resistance in Streptococcus pyogenes is a growing public health concern.
- The M phenotype, mediated by efflux pumps, is one mechanism of resistance.
- Understanding the genetic basis and spread of resistance is crucial for effective treatment.
Purpose of the Study:
- To investigate the prevalence and characteristics of erythromycin-resistant Streptococcus pyogenes strains in Italy.
- To determine the genetic mechanisms (ermAM, mefA) and serotypes associated with erythromycin resistance.
- To assess the geographical distribution of specific resistance phenotypes and genotypes.
Main Methods:
- Analysis of Streptococcus pyogenes strains from Verona, Monza, and Florence for ermAM and mefA genes.
- Erythromycin accumulation assays to detect efflux pump activity.
- Protein T serotyping and pulsed-field gel electrophoresis (PFGE) for DNA macrorestriction profiling.
- Correlation analysis between genetic markers, serotypes, and PFGE profiles.
Main Results:
- The inducible ermAM gene was detected in strains lacking the mefA gene and efflux pump activity, exhibiting similar PFGE profiles.
- Strains with the efflux mechanism and mefA gene belonged to various serotypes, with T4 being isolated in all three cities.
- PFGE analysis using SmaI and SfiI demonstrated a strong correlation between strains of the same serotype.
Conclusions:
- Two distinct mechanisms contribute to erythromycin resistance in Streptococcus pyogenes in Italy: the ermAM gene and the mefA-mediated efflux pump.
- The T4 serotype, associated with the mefA gene, shows a wide geographical distribution across the studied Italian cities.
- Genetic relatedness, as indicated by PFGE, is closely linked to serotype, suggesting clonal spread within specific serotypes.