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Intrinsic reduced susceptibility of serotype 6 Streptococcus pyogenes to fluoroquinolone antibiotics
Rachel C Orscheln1, Dwight R Johnson, Stephen M Olson
1Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110, USA. orscheln_r@kids.wustl.edu
Background:
Fluoroquinolone resistance is common in Staphylococcus aureus, is increasing in Streptococcus pneumoniae, and is reported in Streptococcus pyogenes.
Methods:
We surveyed 384 clinical isolates of S. pyogenes, isolated during 2002-2003, for susceptibility to ciprofloxacin. We performed nucleotide sequencing of the parC and gyrA genes and determined the M/emm type for selected isolates. Additionally, we analyzed M/emm type 6 S. pyogenes isolated during 1918-2003 from diverse locations.
Results:
Of the survey isolates, 10.9% had reduced zones of inhibition to ciprofloxacin in the disk-diffusion test and had elevated minimum inhibitory concentrations to other fluoroquinolones, compared with those of fully susceptible isolates. Of the resistant isolates, 90.5% were M/emm type 6, and all sequenced M/emm type 6 isolates contained a serine-to-alanine substitution at position 79 in parC. Strikingly, the same findings were also present in macrolide-resistant isolates from a recent outbreak of S. pyogenes infection in Pittsburgh and in the Lancefield reference strain of M type 6, which was isolated in 1918, decades before the development of fluoroquinolone antibiotics.
Conclusion:
M/emm type 6 S. pyogenes has intrinsic reduced susceptibility to fluoroquinolones, as a result of a polymorphism in parC. This finding was also demonstrated in erythromycin-resistant M/emm type 6 S. pyogenes, which raises concern for the emergence of multidrug-resistant S. pyogenes.
Insights
Streptococcus pyogenes type 6 exhibits inherent fluoroquinolone resistance due to a parC gene change. This intrinsic resistance, seen even in historical strains, raises concerns for emerging multidrug-resistant strains.
Area of Science:
- Microbiology
- Genetics
- Infectious Diseases
Background:
- Fluoroquinolone resistance is a growing concern in key bacterial pathogens.
- Streptococcus pyogenes, particularly M/emm type 6, shows increasing resistance.
- Understanding resistance mechanisms is crucial for effective treatment.
Purpose of the Study:
- To investigate fluoroquinolone susceptibility in Streptococcus pyogenes clinical isolates.
- To identify genetic mutations associated with fluoroquinolone resistance in S. pyogenes.
- To determine the prevalence and historical context of resistance in M/emm type 6 strains.
Main Methods:
- Surveyed 384 S. pyogenes clinical isolates for ciprofloxacin susceptibility (2002-2003).
- Performed nucleotide sequencing of parC and gyrA genes.
- Determined M/emm types and analyzed historical isolates (1918-2003).
Main Results:
- 10.9% of isolates showed reduced susceptibility to ciprofloxacin.
- 90.5% of resistant isolates were M/emm type 6, with a parC serine-to-alanine substitution.
- This parC polymorphism was present in historical and macrolide-resistant M/emm type 6 strains.
Conclusions:
- M/emm type 6 S. pyogenes possesses intrinsic fluoroquinolone resistance due to a parC polymorphism.
- The presence of this polymorphism in historical strains predates antibiotic development.
- Co-occurrence with macrolide resistance highlights the risk of multidrug-resistant S. pyogenes.
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