Disk diffusion and disk elution tests with A-56268 and erythromycin

Area of Science:

• Microbiology
• Antimicrobial Susceptibility Testing
• Pharmacology

Background:

• Macrolide antibiotics are crucial for treating bacterial infections.
• Accurate susceptibility testing is essential for effective antibiotic selection.
• Erythromycin is a commonly used macrolide, and A-56268 is a newer macrolide requiring evaluation.

Purpose of the Study:

• To compare the antimicrobial activity of A-56268 and erythromycin using disk diffusion and broth dilution methods.
• To determine if A-56268 disk diffusion test interpretive standards can be based on erythromycin standards.
• To assess the efficacy of these macrolides against anaerobic bacteria under different incubation conditions.

Main Methods:

• Disk diffusion tests were performed using 15 microgram disks of A-56268 and erythromycin.
• Broth dilution tests were conducted with incubation in anaerobic jars and aerobic thioglycolate broth.
• Disk elution tests in thioglycolate broth were used to evaluate activity against anaerobes.

Main Results:

• Zones of inhibition for A-56268 disks were comparable to those for erythromycin disks.
• Aerobic incubation of thioglycolate broth demonstrated significantly greater effectiveness of both macrolides against anaerobic bacteria compared to anaerobic incubation.
• Three 15 microgram disks eluted in 5 ml of thioglycolate broth yielded satisfactory results for anaerobic bacteria.

Conclusions:

• Interpretive zone size standards for erythromycin disk tests can likely be applied to A-56268 disk tests.
• Aerobic incubation methods, such as the thioglycolate broth disk elution test, are superior for assessing macrolide activity against anaerobic bacteria.
• A-56268 demonstrates comparable efficacy to erythromycin, suggesting its potential utility in clinical settings, particularly when appropriate testing conditions are employed.