Interpretive criteria for cefamandole and cephalothin disk diffusion susceptibility tests

Area of Science:

• Microbiology
• Clinical Diagnostics
• Antimicrobial Susceptibility Testing

Background:

• Accurate antimicrobial susceptibility testing (AST) is crucial for guiding effective antibiotic therapy.
• Diffusion susceptibility testing is a common method for determining bacterial susceptibility to antibiotics.
• Evaluating the performance of different antibiotic disks is essential for optimizing AST protocols.

Purpose of the Study:

• To establish the accuracy of diffusion susceptibility tests using 30-mug cephalothin disks and 30-mug cefamandole disks.
• To determine if shared interpretive zone standards can be applied to both cephalothin and cefamandole disk diffusion tests.
• To assess the interchangeability of cephalothin and cefamandole disks in routine AST.

Main Methods:

• A multi-center study involving 1,838 clinical isolates.
• Diffusion susceptibility testing was performed using 30-mug cephalothin disks and 30-mug cefamandole disks.
• Zone diameters were measured and compared against established interpretive criteria.

Main Results:

• The study confirmed the accuracy of diffusion susceptibility tests with both 30-mug cephalothin and 30-mug cefamandole disks.
• Identical interpretive zone standards were found to be applicable for tests using either cephalothin or cefamandole disks.
• Despite shared standards, cephalothin and cefamandole disks demonstrated that the two drugs cannot be tested interchangeably.

Conclusions:

• Diffusion susceptibility testing with cephalothin and cefamandole disks is accurate for clinical isolates.
• Shared interpretive criteria enhance consistency in AST when using either cephalothin or cefamandole disks.
• Clinicians and laboratories should be aware that while interpretive standards are similar, cephalothin and cefamandole disks are not interchangeable for AST.