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Macrolide resistance mechanisms and expression of phenotypes among Streptococcus pneumoniae circulating in Italy
A Marchese1, E Tonoli, E A Debbia
1Institute of Microbiology, University of Genoa, Italy.
Abstract:
In Italy, macrolide-resistant pneumococci have been isolated at a rate increasing from 6% in 1993 to 31.7% in 1998. A collection of 161 erythromycin-resistant Streptococcus pneumoniae recovered between 1993 and 1997 has now been phenotypically and genotypically characterized. Approximately 90% of these microorganisms possessed a constitutive MLS(B) mechanism of resistance. PCR detected ermB and mefE genes in strains showing MLS(B) and M phenotypes, respectively. Using pulsed-field gel electrophoresis of chromosomal DNA, one dominant restriction profile and its variations were detected in 51 S. pneumoniae isolates collected from different locations, indicating the circulation of a clone characterized by the possession of a great ability to spread.
Insights
Macrolide resistance in Streptococcus pneumoniae is rising in Italy. Most resistant strains carry the MLS(B) mechanism, suggesting a widespread, highly transmissible clone is circulating.
Area of Science:
- Microbiology
- Molecular Biology
- Epidemiology
Background:
- Macrolide resistance in Streptococcus pneumoniae (pneumococci) has been increasing in Italy.
- From 1993 to 1998, resistance rates rose from 6% to 31.7%.
Purpose of the Study:
- To characterize the phenotypic and genotypic mechanisms of erythromycin resistance in Streptococcus pneumoniae isolates from Italy.
- To investigate the genetic relatedness and spread of resistant pneumococcal strains.
Main Methods:
- Phenotypic characterization of erythromycin resistance.
- Genotypic analysis using Polymerase Chain Reaction (PCR) to detect resistance genes (ermB, mefE).
- Pulsed-field gel electrophoresis (PFGE) of chromosomal DNA to assess strain relatedness.
Main Results:
- 161 erythromycin-resistant Streptococcus pneumoniae isolates were analyzed.
- Approximately 90% exhibited a constitutive MLS(B) resistance mechanism.
- PCR confirmed ermB genes in MLS(B) strains and mefE genes in M phenotype strains.
- PFGE revealed a dominant restriction profile in 51 isolates, indicating a common, widespread clone.
Conclusions:
- A significant increase in macrolide-resistant pneumococci has been observed in Italy.
- The constitutive MLS(B) mechanism, mediated by the ermB gene, is the predominant resistance mechanism.
- Evidence suggests the circulation of a highly transmissible clone of Streptococcus pneumoniae responsible for spreading macrolide resistance.