Proposed disk diffusion susceptibility criteria for ofloxacin

Area of Science:

• Microbiology
• Clinical Microbiology
• Antimicrobial Susceptibility Testing

Background:

• Disk diffusion is a common method for assessing bacterial susceptibility to antibiotics.
• Establishing reliable breakpoint criteria is crucial for accurate interpretation of these tests.
• Ofloxacin is a widely used fluoroquinolone antibiotic.

Purpose of the Study:

• To establish tentative breakpoint criteria for the disk diffusion method for ofloxacin.
• To correlate minimum inhibitory concentrations (MICs) with zone diameters for ofloxacin disk diffusion.

Main Methods:

• Correlated MIC values with 1-, 3-, and 5-microgram disk inhibitory zone diameters.
• Tested 638 bacterial isolates from 36 different species.
• Proposed breakpoint criteria based on the correlation analysis.

Main Results:

• Recommended the use of 5-microgram disks for ofloxacin susceptibility testing.
• Defined breakpoints: Susceptible (MIC ≤ 2.0 µg/ml) ≥ 16 mm zone diameter.
• Defined breakpoints: Intermediate (MIC = 4.0 µg/ml) 13–15 mm zone diameter; Resistant (MIC ≥ 8.0 µg/ml) ≤ 12 mm zone diameter.

Conclusions:

• The proposed breakpoints provide a standardized method for interpreting ofloxacin disk diffusion tests.
• These criteria facilitate accurate determination of bacterial resistance and susceptibility to ofloxacin.
• Implementation of these breakpoints can improve clinical guidance for ofloxacin therapy.