Caspofungin susceptibility testing is a method used to determine the effectiveness of caspofungin, an echinocandin antifungal agent, against various fungal pathogens. The testing assesses the minimum inhibitory concentration (MIC) of caspofungin required to inhibit fungal growth.

Testing Methods

• Broth Microdilution: This involves serially diluting caspofungin in a broth medium and inoculating it with the fungus. The MIC is determined by observing the lowest concentration that prevents visible growth.
• Agar Disk Diffusion: A disk impregnated with caspofungin is placed on an agar plate inoculated with the fungus. The zone of inhibition around the disk is measured to estimate susceptibility.

Standards and Guidelines

• Clinical and Laboratory Standards Institute (CLSI) provides guidelines for performing broth microdilution testing and interpreting MIC results.
• European Committee on Antimicrobial Susceptibility Testing (EUCAST) offers alternative guidelines for susceptibility testing.

Interpretation of Results

• Susceptible: The MIC falls within a range indicating that caspofungin is effective at standard dosages.
• Intermediate: The MIC is at a threshold where the efficacy may vary and might require higher doses or alternative treatments.
• Resistant: The MIC is above the range where caspofungin is considered effective, indicating resistance.

Quality Control

• Testing must include control strains to ensure the accuracy and reliability of the results. CLSI and EUCAST specify control organisms and acceptable ranges for testing.

Clinical Relevance

• Accurate susceptibility testing is crucial for guiding effective treatment, especially given the rise of antifungal resistance.

Understanding caspofungin susceptibility is essential for optimizing antifungal therapy and managing resistance patterns effectively.