Interpretive criteria for the agar diffusion susceptibility test with enoxacin

Area of Science:

• Microbiology
• Antimicrobial Susceptibility Testing

Background:

• Accurate antimicrobial susceptibility testing (AST) is crucial for guiding effective treatment of infectious diseases.
• Enoxacin is a fluoroquinolone antibiotic used to treat various bacterial infections.
• Standardization of AST methods ensures reliable interpretation of results.

Purpose of the Study:

• To determine the correlation between Minimum Inhibitory Concentration (MIC) and inhibition zone diameters for enoxacin discs.
• To evaluate the performance of different enoxacin disc concentrations (5 and 10 µg) and AST methods (ICS and Kirby-Bauer).
• To establish reliable zone interpretation criteria for enoxacin susceptibility testing.

Main Methods:

• Regression analysis was performed on 300 clinical isolates from 15 species.
• Enoxacin discs (5 and 10 µg) were tested using both the International Clinical Standards (ICS) and Kirby-Bauer methods on Iso-Sensitest and Mueller-Hinton agars.
• MIC breakpoints and zone cut-off points were calculated and compared.

Main Results:

• Correlation between MIC and zone diameter decreased with higher enoxacin disc content and with the Kirby-Bauer method.
• No major errors in zone interpretation were found using preliminary breakpoints.
• Minor errors occurred in 3.7% (ICS, 5 µg discs) and 11.0% (Kirby-Bauer, 10 µg discs).

Conclusions:

• Recommended zone interpretations for enoxacin susceptibility testing were proposed for both ICS and Kirby-Bauer methods.
• The study provides guidance for accurate interpretation of enoxacin susceptibility results in clinical microbiology laboratories.
• Optimized disc concentrations and methods can improve the reliability of AST for enoxacin.