Rapid antimicrobial susceptibility test using tetrazolium reduction

Area of Science:

• Clinical Microbiology
• Diagnostic Technology
• Antimicrobial Resistance

Background:

• Standard antimicrobial susceptibility testing methods can be time-consuming.
• Rapid diagnostics are crucial for timely clinical decision-making and effective treatment of bacterial infections.
• Existing rapid methods may have limitations in accuracy or cost-effectiveness.

Purpose of the Study:

• To develop and evaluate a rapid antimicrobial susceptibility testing (AST) method.
• To assess the accuracy and efficiency of the new method compared to established reference techniques.
• To determine the potential economic benefits of the rapid AST method.

Main Methods:

• A modified microdilution procedure with a high inoculum (10^7 bacteria/ml) was employed.
• Antimicrobial activity was detected within 4 hours using a tetrazolium salt indicator accelerated by phenazine methosulfate.
• Results were compared against the Bauer-Kirby and agar dilution methods using 1,126 bacterial isolates and 10 antimicrobial agents.

Main Results:

• The rapid method demonstrated a low discrepancy rate (6.0% total) compared to agar dilution, with 2.3% very major and 0.7% major discrepancies.
• Specific organism-antimicrobial combinations, including Staphylococcus aureus and Acinetobacter sp. with chloramphenicol, showed higher discrepancy rates.
• The method was found to be economical compared to Autobac 1 and Bauer-Kirby procedures.

Conclusions:

• The developed rapid AST method offers a viable alternative to conventional techniques, providing timely results.
• Minor adjustments in antibiotic concentrations or inoculum size may further improve accuracy for certain combinations.
• The method presents a cost-effective and efficient diagnostic tool for clinical microbiology laboratories.