Cefotetan Susceptibility Testing 

Cefotetan is a second-generation cephamycin-class cephalosporin with broad-spectrum activity against Gram-negative and select Gram-positive bacteria. It exhibits notable stability against some β-lactamases, including those produced by Bacteroides fragilis, but remains susceptible to hydrolysis by extended-spectrum β-lactamases (ESBLs) and carbapenemases. Cefotetan is primarily used for anaerobic infections, intra-abdominal infections, gynecologic infections, and surgical prophylaxis.

Testing Methodologies

The susceptibility of cefotetan is determined using Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines, employing the following methodologies:

• Broth Microdilution (BMD) Method:
  • Considered the gold standard for minimum inhibitory concentration (MIC) determination.
  • Conducted in cation-adjusted Mueller-Hinton broth (CAMHB) under anaerobic or aerobic conditions, depending on the pathogen.
• Etest (Gradient Strip) Method:
  • Utilizes a concentration gradient strip impregnated with cefotetan.
  • Provides direct MIC determination, particularly useful for slow-growing anaerobes.
• Automated Susceptibility Testing Systems:
  • Platforms such as VITEK 2, BD Phoenix, and Microscan determine cefotetan MIC values.

Application and Clinical Relevance

• Treatment of Anaerobic and Polymicrobial Infections:
  • Cefotetan is used for intra-abdominal infections, pelvic infections, aspiration pneumonia, and surgical prophylaxis.
• Detection and Monitoring of Resistance Mechanisms:
  • Resistance mechanisms include ESBL production (CTX-M, TEM, SHV), carbapenemases (KPC, NDM, VIM, OXA-48, IMP), and porin modifications.
• Surveillance and Resistance Trends:
  • Continuous susceptibility testing is essential to monitor emerging resistance trends in anaerobes and facultative anaerobes.

Cefotetan susceptibility testing is crucial for effective treatment of anaerobic and polymicrobial infections. Broth microdilution and disk diffusion methods remain primary approaches, while automated systems offer high-throughput results with limitations in anaerobic detection.