Use of a predictor panel to evaluate susceptibility testing methods for ampicillin-sulbactam

Area of Science:

• Clinical Microbiology
• Antimicrobial Susceptibility Testing

Background:

• Beta-lactamase-producing bacteria pose a challenge for antibiotic efficacy.
• Accurate susceptibility testing is crucial for guiding antibiotic therapy.

Purpose of the Study:

• To evaluate the accuracy of various susceptibility tests for ampicillin-sulbactam against clinical isolates producing diverse beta-lactamases.
• To identify optimal testing parameters for reliable ampicillin-sulbactam susceptibility determination.

Main Methods:

• Utilized a predictor panel of clinical isolates with varying beta-lactamase production.
• Assessed ampicillin-sulbactam in broth and agar dilution tests with different ratios and concentrations.
• Examined disk diffusion tests using various ampicillin-sulbactam disk strengths.

Main Results:

• Broth microdilution MICs showed less than twofold average differences across tested combinations.
• The 20/10 microgram ampicillin-sulbactam disk demonstrated superior separation of susceptible and resistant strains.
• This disk also achieved the highest agreement with broth microdilution MICs.
• Agar and broth microdilution MICs exhibited greater than twofold average discrepancies, necessitating distinct interpretive criteria.

Conclusions:

• A predictor panel effectively identified accurate susceptibility testing parameters for ampicillin-sulbactam.
• The 20/10 microgram disk diffusion test is recommended for reliable susceptibility testing.
• Separate interpretive criteria are required for agar and broth microdilution methods.