Caspofungin Susceptibility Testing 

Caspofungin is an echinocandin antifungal agent used to treat invasive fungal infections, particularly those caused by Candida species and Aspergillus species. It inhibits β-1,3-D-glucan synthase, an essential enzyme for fungal cell wall synthesis, leading to cell wall disruption and fungal cell death. Susceptibility testing for caspofungin is performed to evaluate its activity against fungal isolates, guide antifungal therapy, and monitor resistance trends.

Content:

• Testing Methods:
  • Broth Microdilution (Gold Standard):
    • Recommended by CLSI (Clinical and Laboratory Standards Institute) and EUCAST for determining the Minimum Inhibitory Concentration (MIC).
    • The MIC is defined as the lowest concentration of caspofungin that produces significant inhibition (e.g., ≥50% reduction) of fungal growth.
  • E-test (Gradient Diffusion):
    • A strip containing a gradient of caspofungin concentrations is placed on an agar plate inoculated with the fungal isolate
• • Disk Diffusion:
    • Rarely used for caspofungin because of its inconsistent correlation with MIC results.

Application:

• Clinical Use:
  • Caspofungin is used to treat:
    • Invasive candidiasis, including candidemia.
    • Esophageal candidiasis.
    • Empirical therapy for suspected fungal infections in febrile neutropenic patients.
    • Invasive aspergillosis in patients intolerant of or refractory to other therapies.
• Antifungal Stewardship:
  • Ensures targeted therapy by confirming susceptibility in fungal pathogens.
  • Promotes de-escalation to less costly antifungals when appropriate.
  • Prevents unnecessary use of echinocandins in resistant cases, reducing selective pressure for resistance.
• Epidemiological Surveillance:
  • Tracks resistance trends, especially in Candida glabrata and Candida parapsilosis.
  • Identifies emerging resistance due to FKS mutations in clinical isolates.

Caspofungin susceptibility testing is a critical diagnostic tool for managing invasive fungal infections caused by Candida species. Broth microdilution is the gold standard method for determining MICs, while E-tests offer a convenient alternative in some settings.