Susceptibility testing quality control studies with fosfomycin tromethamine

Area of Science:

• Microbiology
• Clinical Pharmacy
• Antimicrobial Susceptibility Testing

Background:

• Fosfomycin tromethamine is a crucial antibiotic for treating various infections.
• Standardized quality control (QC) parameters are essential for reliable antimicrobial susceptibility testing (AST).
• Previous studies have indicated variability in fosfomycin susceptibility testing methods.

Purpose of the Study:

• To define and propose validated quality control ranges for fosfomycin tromethamine susceptibility testing.
• To evaluate the reproducibility of different AST methods for fosfomycin tromethamine.
• To provide essential data for clinical laboratories performing AST.

Main Methods:

• Disk diffusion testing was performed using Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923.
• Agar dilution testing was conducted with Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 29213, Pseudomonas aeruginosa ATCC 27853, and Enterococcus faecalis ATCC 29212.
• Broth microdilution was assessed for reproducibility.

Main Results:

• Proposed disk diffusion QC ranges: E. coli (22-30 mm), S. aureus (25-33 mm).
• Proposed agar dilution QC ranges: E. coli (0.5-2.0 µg/mL), S. aureus (0.5-4.0 µg/mL), P. aeruginosa (2.0-8.0 µg/mL), E. faecalis (32-128 µg/mL).
• Broth microdilution testing demonstrated poor reproducibility.

Conclusions:

• Disk diffusion and agar dilution methods are suitable for fosfomycin tromethamine susceptibility testing with defined QC ranges.
• Broth microdilution is not recommended for fosfomycin tromethamine susceptibility testing due to lack of reproducibility.
• These validated QC ranges will enhance the accuracy and reliability of fosfomycin susceptibility testing in clinical laboratories.