Anidulafungin Susceptibility Testing 

Anidulafungin is an echinocandin antifungal agent used to treat invasive fungal infections, particularly those caused by Candida species. It works by inhibiting β-1,3-D-glucan synthase, an enzyme necessary for fungal cell wall synthesis. This mechanism provides fungicidal activity against most Candida species but only fungistatic activity against Aspergillus. Anidulafungin susceptibility testing is performed to determine its efficacy against fungal isolates, guide treatment, and monitor resistance trends.

Content:

• Testing Methods:
  • Broth Microdilution (Gold Standard):
    • CLSI and EUCAST recommend broth microdilution methods to determine the Minimum Inhibitory Concentration (MIC).
    • The MIC is defined as the lowest concentration of anidulafungin that causes a significant reduction (≥50%) in fungal growth compared to a control.
  • E-test (Gradient Diffusion):
    • A gradient strip containing anidulafungin is placed on an agar plate inoculated with the fungal isolate.
• • Automated Testing Systems:
    • Some automated systems, like Sensititre YeastOne, can perform echinocandin MIC testing with high reproducibility.

Application:

• Clinical Use:
  • Anidulafungin is primarily used to treat:
    • Invasive candidiasis, including candidemia.
    • Esophageal candidiasis (although oral therapy is often preferred).
    • Empirical therapy for suspected fungal infections in neutropenic patients.
• Antifungal Stewardship:
  • Helps ensure appropriate use of anidulafungin and reduces unnecessary antifungal therapy.
  • Supports the de-escalation of echinocandins to other antifungal classes once susceptibility results are available.
• Epidemiological Surveillance:
  • Tracks resistance trends, particularly in Candida glabrata and other echinocandin-resistant species.
  • Identifies emerging resistance mechanisms, such as FKS mutations.

Anidulafungin susceptibility testing is an essential tool for managing invasive fungal infections caused by Candida species. Broth microdilution is the gold standard method, with MIC results interpreted using CLSI or EUCAST breakpoints.