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Published on: July 9, 2012
Detection of penicillin tolerance in Streptococcus pyogenes
1Department of Medical Microbiology, University Hospital, Leiden, The Netherlands.
Journal of Medical Microbiology
|March 1, 1993
Summary
Penicillin tolerance in Streptococcus pyogenes is identified by comparing minimal bactericidal concentration (MBC) and minimal inhibitory concentration (MIC) ratios. Stationary phase cultures are crucial for accurately detecting moderate penicillin tolerance in these bacteria.
Area of Science:
- Microbiology
- Bacteriology
- Antimicrobial Resistance
Background:
- Streptococcus pyogenes, or group A streptococci, poses significant public health challenges.
- Understanding penicillin tolerance is crucial for effective treatment strategies.
- Existing methods for assessing bacterial tolerance have limitations.
Purpose of the Study:
- To evaluate traditional and novel methods for determining penicillin tolerance in Streptococcus pyogenes.
- To investigate the impact of growth phase on the accurate assessment of bacterial tolerance.
- To establish reliable criteria for identifying penicillin-tolerant strains of S. pyogenes.
Main Methods:
- Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) assays were performed on S. pyogenes.
- Penicillin tolerance was assessed using cell-lysis, beta-lactamase disk, and replication methods.
- Cultures were analyzed during both mid-logarithmic and stationary growth phases.
Main Results:
- Two distinct groups of S. pyogenes strains were identified based on penicillin tolerance levels: highly tolerant and moderately tolerant.
- Moderate tolerance was underestimated when using rapidly growing cultures for MIC and MBC determinations.
- The MBC/MIC ratio exceeded 100 for tolerant strains, with tolerance percentages varying by growth phase.
Conclusions:
- The MBC/MIC ratio is a key indicator for distinguishing penicillin-tolerant S. pyogenes strains.
- Stationary phase cultures are essential for accurate detection of moderate penicillin tolerance.
- Recommended methods for screening tolerance include cell-lysis, beta-lactamase disk, and replication assays, alongside MBC/MIC ratio determination.
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