Evaluation of the micro-media system for quantitative antimicrobial drug susceptibility testing: a collaborative...

Area of Science:

• Clinical Microbiology
• Pharmaceutical Sciences
• Laboratory Medicine

Background:

• Micro-Media Systems (MMS) developed a novel procedure for preparing and distributing frozen microdilution trays for antimicrobial susceptibility testing.
• These trays are prepared at distribution centers to supply clinical laboratories, offering a convenient method for antibiotic dilution testing.

Purpose of the Study:

• To evaluate the efficacy and reproducibility of microdilution trays prepared by Micro-Media Systems (MMS).
• To compare the minimal inhibitory concentrations (MICs) obtained from microdilution trays with standard tube dilution methods.

Main Methods:

• A collaborative study involved preparing microdilution trays at three MMS distribution centers.
• Microdilution MICs were determined and compared against results from standard tube dilution tests.
• Reproducibility was assessed for both inter- and intralaboratory variations.

Main Results:

• Microdilution and standard tube dilution methods yielded equivalent results for gram-positive cocci.
• For gram-negative bacilli, microdilution MICs were typically one doubling dilution lower than standard tube dilution MICs.
• Inter- and intralaboratory reproducibility for both macro- and microdilution techniques were satisfactory, with over 96% of endpoints within +/-1 log(2) dilution intervals.

Conclusions:

• The developed microdilution tray method is a viable and reproducible alternative for antimicrobial susceptibility testing in clinical laboratories.
• The method demonstrates good agreement with standard techniques, particularly for gram-positive organisms, and acceptable performance for gram-negative bacilli.
• The frozen microdilution tray system offers a practical solution for consistent and reliable antimicrobial testing across different laboratory settings.