Simplified plate diffusion system for microbial assays of antibiotics

Area of Science:

• Microbiology
• Analytical Chemistry
• Pharmaceutical Science

Background:

• Microbial assays are crucial for determining antibiotic potency.
• Existing methods, like the AOAC diffusion procedure, can be resource-intensive.
• There is a need for efficient and accurate antibiotic testing protocols.

Purpose of the Study:

• To present a simplified protocol for microbial antibiotic assays using a plate diffusion system.
• To evaluate the accuracy and precision of this simplified system against the official AOAC method.
• To assess the performance of single-plate, two-plate, and three-plate options within the simplified design.

Main Methods:

• Development of a plate diffusion system allowing standard curves and unknowns on the same plate.
• Comparison of the simplified system with the official AOAC diffusion procedure.
• Testing of four antibiotics: bacitracin, chlortetracycline, oxytetracycline, and streptomycin.
• Statistical analysis of coefficients of variation (CVs) for different plate configurations.

Main Results:

• The simplified plate diffusion system demonstrated accuracy and precision comparable to the AOAC method.
• CVs for the AOAC design ranged from 1.4% to 10.3% (mean 4.5%).
• CVs for the simplified design's 2-plate option were 2.5% to 6.8% (mean 4.3%), and the 3-plate option showed 1.2% to 5.0% (mean 3.0%), indicating high precision.

Conclusions:

• The presented simplified plate diffusion protocol is a viable alternative to the official AOAC method for microbial antibiotic assays.
• The simplified system offers comparable accuracy and precision, potentially with increased efficiency.
• The two-plate and three-plate options of the simplified design provide excellent precision for antibiotic quantification.