Echinocandins (e.g., caspofungin) are active against Candida but not Cryptococcus neoformans. The reason is:
- A Cryptococcus lacks a cell wall, making it immune to cell-wall-active agents
- B Cryptococcus produces extracellular β-glucanase that inactivates echinocandin molecules
- C Cryptococcus neoformans has intrinsic low expression of the FKS1 gene encoding β-1,3-glucan synthase, the echinocandin target ✓
- D The thick polysaccharide capsule of Cryptococcus prevents echinocandin penetration to the cell wall
Correct answer: C. Cryptococcus neoformans has intrinsic low expression of the FKS1 gene encoding β-1,3-glucan synthase, the echinocandin target
Explanation
Echinocandins inhibit β-1,3-glucan synthase (encoded by FKS1/FKS2 genes), an enzyme synthesising the major structural polysaccharide of the Candida and Aspergillus cell wall. Cryptococcus neoformans has intrinsically low levels of the FKS1-encoded enzyme and minimal β-1,3-glucan in its cell wall; consequently, echinocandins have negligible activity against Cryptococcus. Treatment of cryptococcal meningitis relies on amphotericin B plus flucytosine (induction) followed by fluconazole (consolidation/maintenance).
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.