A modified Kirby-Bauer disc diffusion (mKB) method for accurately testing tigecycline susceptibility: a nation-wide...

Area of Science:

• Clinical Microbiology
• Antimicrobial Resistance
• Infectious Diseases

Background:

• Tigecycline is vital for treating multidrug-resistant infections.
• Conventional antimicrobial susceptibility testing (AST) methods often yield inaccurate tigecycline susceptibility results, potentially leading to treatment failures.
• Accurate AST is essential for effective clinical antimicrobial therapy.

Purpose of the Study:

• To evaluate a modified Kirby-Bauer disc diffusion (mKB) method for tigecycline susceptibility testing.
• To determine if the mKB method provides more accurate results compared to the standard Kirby-Bauer disc diffusion (sKB) method.
• To establish a reliable method for reporting tigecycline susceptibility in clinical practice.

Main Methods:

• A total of 4271 nonduplicate clinical strains were tested.
• The modified Kirby-Bauer disc diffusion (mKB) method was compared against the standard Kirby-Bauer disc diffusion (sKB) method and the reference broth microdilution (BMD) method.
• Categorical agreement (CA), minor errors (mE), major errors (ME), and very major errors (VME) were used for evaluation.

Main Results:

• The mKB method demonstrated higher categorical agreement (CA) than the sKB method for both *Acinetobacter baumannii* (90.6% vs 44.8%) and *Enterobacterales* (87.2% vs 52.0%) when compared to the reference BMD method.
• The mKB method met acceptability criteria for major errors (ME) and very major errors (VME) for both bacterial groups, unlike the sKB method.
• The mKB method showed significantly lower minor errors (mE) compared to the sKB method for *A. baumannii* (9.0% vs 45.2%).

Conclusions:

• The modified Kirby-Bauer disc diffusion (mKB) method provides more accurate bacterial susceptibility testing for tigecycline compared to the standard Kirby-Bauer disc diffusion (sKB) method.
• The mKB method is a reliable alternative for tigecycline susceptibility testing, especially for strains yielding intermediate or resistant results with the sKB method.
• Utilizing the mKB method can help ensure accurate reporting of tigecycline susceptibility, thereby improving clinical antimicrobial therapies.