Comparison of cefadroxil and cephalothin disk susceptibility test results

Area of Science:

• Microbiology
• Clinical Pharmacy
• Antimicrobial Susceptibility Testing

Background:

• Cefadroxil and cephalothin are first-generation cephalosporin antibiotics.
• Accurate in vitro susceptibility testing is crucial for guiding antibiotic therapy.
• Evaluating the interchangeability of antimicrobial disks can streamline laboratory workflows.

Purpose of the Study:

• To assess the interchangeability of cefadroxil and cephalothin disk diffusion tests for bacterial susceptibility.
• To determine if cephalothin disk testing can reliably predict cefadroxil susceptibility.
• To identify bacterial species where cefadroxil and cephalothin testing yield significantly different results.

Main Methods:

• Diffusion susceptibility tests were performed using 30-micrograms cefadroxil and 30-micrograms cephalothin disks.
• Standardized zone size interpretive criteria were applied for both agents.
• The study analyzed data from 904 bacterial isolates representing various species.

Main Results:

• Identical zone size interpretive criteria (≤14 mm for resistance, ≥18 mm for susceptibility) were recommended for both cefadroxil and cephalothin.
• Significant discrepancies between cefadroxil and cephalothin testing were noted for Haemophilus influenzae, Listeria monocytogenes, and methicillin-resistant staphylococci.
• For other bacterial species tested, cefadroxil susceptibility could be reliably predicted using cephalothin disk diffusion or MIC results.

Conclusions:

• Cephalothin disk diffusion testing can be used interchangeably with cefadroxil for most bacterial species.
• Specific exceptions, including H. influenzae, L. monocytogenes, and MRSA, require distinct testing or interpretation.
• The findings support the potential for using cephalothin as a surrogate for cefadroxil susceptibility testing in routine clinical microbiology.