Related Experiment Video
Updated: Aug 4, 2026
One-day Workflow Scheme for Bacterial Pathogen Detection and Antimicrobial Resistance Testing from Blood Cultures
Published on: July 9, 2012
Detection of penicillin tolerance in Streptococcus pyogenes
1Department of Medical Microbiology, University Hospital, Leiden, The Netherlands.
Abstract:
Three traditional assays were used to determine the minimal bactericidal concentration (MBC) and minimal inhibitory concentration (MIC) for Streptococcus pyogenes (group A streptococci) in two phases of growth and the time taken to kill the organisms. Three other methods were used for the determination of penicillin tolerance: a cell-lysis assay, the beta-lactamase disk method and the replication method. Twenty strains, comprising penicillin-tolerant clinical isolates and two laboratory mutants, were used to evaluate the six tests. Results indicated that two groups of S. pyogenes can be distinguished--four highly tolerant and three moderately tolerant strains. The moderately tolerant strains were not recognised when rapidly growing instead of stationary cultures were used for the MBC and MIC determinations. The MBC/MIC ratio for tolerant strains was > 100. Tolerance percentage ranged from 0.30 to 1.07 and 0.29 to 3.96 for cultures in the mid-logarithmic and stationary phases of growth, respectively. The cell-lysis assay, the beta-lactamase disk method and the replication method may be used to screen for tolerance. Detection of high or moderate tolerance by determining the MBC/MIC ratio for mid-logarithmic or stationary cultures is recommended.
Insights
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.
Related Concept Videos
01:27Production of Antibiotics
01:25Mechanism of Antibiotic Resistance in MRSA
01:23Inhibitors of Gram-positive Cell Wall Synthesis