[Comparative in vitro activity of new oral macrolides against Streptococcus pyogenes strains]
1Unidad de Microbiología, Facultad de Medicina, Universidad de Chile, Santiago de Chile.
Abstract:
Some recently introduced macrolides have several clinical advantages over erythromycin. Azithrommcin, a prototype of these new macrolides could be a good alternative for the treatment of streptococcal pharyngitis, even over penicillin, whose failure rate can be as high as 30%. The aim of this study was to evaluate the in vitro susceptibility of 120 strains of S pyogenes isolated between 1990 and 1992 (40 per year), from diverse infections (specially tonsillitis). We determined Minimal Inhibitory Concentrations (MIC) of azithromycin, clarithromycin, roxithromycin, erythromycin and penicillin using the agar dilution method and the Minimal Bactericidal Concentration (MBC) by tube dilution for azythromycin and erythromycin. The MIC 90 for the new macrolides ranged from 0.03 to 0.12 microgram/ml, and was 0.03 microgram/ml for erythromycin and penicillin (not different). All strains were susceptible to all antibiotics and the date of isolation did not influence susceptibility. The MBC for azithromycin was 0.12 microgram/ml (identical to its MIC), which demonstrates the bactericidal effect of this antibiotic. It is concluded that this in vitro data supports the potential role of these new macrolides in the treatment of streptococcal infections.
Insights
New macrolides like azithromycin show strong in vitro effectiveness against Streptococcus pyogenes, offering a promising alternative to penicillin for treating streptococcal pharyngitis and other infections.
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Erythromycin has limitations in treating streptococcal pharyngitis, with penicillin failure rates up to 30%.
- Newer macrolides offer potential clinical advantages over erythromycin.
Purpose of the Study:
- To evaluate the in vitro susceptibility of Streptococcus pyogenes strains to new macrolides and penicillin.
- To assess the efficacy of azithromycin and erythromycin in terms of Minimal Bactericidal Concentration (MBC).
Main Methods:
- Agar dilution method to determine Minimal Inhibitory Concentrations (MIC) for azithromycin, clarithromycin, roxithromycin, erythromycin, and penicillin.
- Tube dilution method to determine MBC for azithromycin and erythromycin.
- Testing of 120 S. pyogenes strains isolated between 1990-1992.
Main Results:
- MIC90 values for new macrolides ranged from 0.03 to 0.12 µg/ml; erythromycin and penicillin MIC90 was 0.03 µg/ml.
- All tested S. pyogenes strains were susceptible to all antibiotics, with no influence from isolation date.
- Azithromycin demonstrated bactericidal activity with an MBC of 0.12 µg/ml, identical to its MIC.
Conclusions:
- In vitro data support the use of new macrolides, including azithromycin, for treating streptococcal infections.
- Azithromycin's potent activity and bactericidal effect make it a viable alternative to penicillin for streptococcal pharyngitis.
