Related Experiment Videos
Penicillin tolerance of human isolates of group C streptococci
Abstract:
Seventeen clinical isolates of group C streptococci were tested for penicillin tolerance. Sixteen of the strains showed penicillin tolerance with a 32-fold or greater difference between the minimal inhibitory concentration and the minimal bactericidal concentration. Synergism was demonstrated with a combination of penicillin and gentamicin for all 17 strains tested. The rate of antibiotic killing was measured for five of the streptococcal strains by using the combination of penicillin and gentamicin. All isolates were killed within 5 h with the combination, but viable organisms were recovered after 48 h when either drug was used alone. Our study suggests that penicillin tolerance with group C streptococci may occur frequently and may account for the poor outcome of serious group C streptococcal infections tested with penicillin alone.
Insights
Penicillin tolerance is common in group C streptococci infections. Combining penicillin with gentamicin effectively kills these bacteria, suggesting a better treatment approach for serious infections.
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Group C streptococci are significant human pathogens.
- Penicillin is a primary antibiotic for streptococcal infections.
- Previous studies have not fully characterized penicillin tolerance in group C streptococci.
Purpose of the Study:
- To investigate the prevalence of penicillin tolerance in clinical isolates of group C streptococci.
- To evaluate the synergistic effect of penicillin and gentamicin against these strains.
- To assess the bactericidal activity of the combination therapy.
Main Methods:
- Testing 17 clinical isolates of group C streptococci for penicillin tolerance.
- Determining the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC).
- Evaluating the synergistic activity of penicillin and gentamicin in vitro.
- Measuring the rate of bacterial killing using time-kill assays.
Main Results:
- Sixteen out of 17 isolates (94%) exhibited penicillin tolerance (MIC/MBC ratio ≥ 32).
- Penicillin and gentamicin demonstrated synergistic killing of all tested strains.
- The combination therapy eradicated all isolates within 5 hours, while monotherapy failed within 48 hours.
Conclusions:
- Penicillin tolerance is a frequent characteristic of group C streptococci.
- The combination of penicillin and gentamicin offers a potent bactericidal effect.
- This synergy may explain treatment failures with penicillin monotherapy in severe group C streptococcal infections.