Imipenem susceptibility testing with a commercially prepared dry-format microdilution tray

Area of Science:

• Clinical Microbiology
• Antimicrobial Susceptibility Testing
• Infectious Diseases

Background:

• Accurate antimicrobial susceptibility testing (AST) is crucial for guiding effective treatment of bacterial infections.
• Standardized methods for AST, such as microdilution and agar dilution, are essential for reliable results.
• Imipenem is a broad-spectrum carbapenem antibiotic used to treat serious bacterial infections.

Purpose of the Study:

• To evaluate the accuracy and stability of imipenem Minimum Inhibitory Concentrations (MICs) generated using Sensititre microdilution trays.
• To assess the in vitro activity of imipenem against a large collection of clinical bacterial isolates.

Main Methods:

• Comparative analysis of imipenem MICs determined by Sensititre microdilution trays and standard agar dilution assays.
• Evaluation of imipenem stability in Sensititre trays stored at room temperature over five months using Pseudomonas aeruginosa ATCC 27853.
• Determination of imipenem MICs for 890 clinical bacterial isolates using microdilution testing.

Main Results:

• MICs from Sensititre trays correlated within +/- 1 twofold dilution for 94% of 226 bacterial isolates compared to agar dilution.
• Imipenem demonstrated stable biological activity over five months of storage in Sensititre trays.
• High in vitro activity of imipenem was observed, with only 4% of 890 clinical isolates exhibiting MICs >= 16 µg/mL (indicating resistance).

Conclusions:

• Sensititre microdilution trays provide accurate and reliable MIC values for imipenem when compared to standard agar dilution methods.
• Imipenem exhibits excellent stability in Sensititre trays, supporting their use for routine AST.
• Imipenem maintains potent in vitro activity against a wide range of clinical bacterial isolates, suggesting its continued clinical utility.