Methods for storage of antimicrobial effectiveness test inoculum suspensions below freezing

Area of Science:

• Microbiology
• Pharmaceutical Sciences

Background:

• Accurate antimicrobial effectiveness testing relies on stable microbial inoculum.
• Preservation methods for microbial stock cultures are essential for consistent test results.

Purpose of the Study:

• To evaluate the suitability of sub-zero storage for common antimicrobial test inoculum organisms.
• To compare different cryoprotective solutions for preserving microbial viability.

Main Methods:

• Inoculum suspensions of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans were prepared.
• Suspensions were stored at -50°C for 6 months using various cryoprotective agents: 10% dextrose, distilled water, 15% glycerol, and 7.5% dimethyl sulfoxide (DMSO).
• Viability and suitability for antimicrobial effectiveness testing were assessed.

Main Results:

• Inoculum suspensions were most stable when prepared with 10% dextrose.
• After 6 months of storage at -50°C, 10% dextrose maintained the viability of all tested organisms.
• Microbial suspensions preserved in 10% dextrose were suitable for antimicrobial effectiveness testing.

Conclusions:

• Ten percent dextrose is a suitable cryoprotective agent for storing antimicrobial effectiveness test inoculum organisms.
• Long-term storage at -50°C using 10% dextrose ensures inoculum viability for preservative efficacy testing.
• This method supports the reliability of antimicrobial effectiveness assays.