Regression analyses for cefoperazone on Mueller-Hinton agar and DST agar

Area of Science:

• Microbiology
• Clinical Bacteriology
• Antimicrobial Susceptibility Testing

Background:

• Accurate antimicrobial susceptibility testing (AST) is crucial for guiding effective antibiotic therapy.
• Establishing reliable correlations between different AST methods, such as agar diffusion and broth dilution, is essential for clinical laboratories.
• Agar diffusion methods, like the Bauer-Kirby method, provide zone diameters, while broth dilution determines the minimal inhibitory concentration (MIC).

Purpose of the Study:

• To establish a quantitative relationship between zone diameter from agar diffusion and MIC from broth dilution for antibiotic susceptibility testing.
• To evaluate the impact of different agar media, specifically Mueller-Hinton and DST-Oxoid agars, on zone diameter measurements.
• To compare the efficacy of DST agar versus Mueller-Hinton agar in discriminating bacterial susceptibility breakpoints.

Main Methods:

• Tested 142 gram-positive and 161 gram-negative bacterial strains.
• Employed both agar diffusion with antibiotic disks (30 µg/ml) and broth dilution methods.
• Analyzed zone diameters on Mueller-Hinton and DST-Oxoid agars.
• Determined first and second-order regression lines and correlation coefficients (R) using computer programming.

Main Results:

• Achieved acceptable correlation coefficients (R = 0.84–0.92) between zone diameter and MIC.
• Observed differences in regression lines that corresponded to clinically significant resistant/susceptible categories.
• DST agar demonstrated a better ability to differentiate breakpoints compared to Mueller-Hinton agar when using the Bauer-Kirby method.

Conclusions:

• A strong correlation exists between agar diffusion zone diameters and broth dilution MICs, validating both methods for bacterial susceptibility assessment.
• DST agar is recommended over Mueller-Hinton agar for agar diffusion testing to improve the accurate categorization of bacterial susceptibility.
• The findings support the reliable interpretation of antibiotic susceptibility data, aiding in the selection of appropriate antimicrobial agents.