confers_resistance_to_antibiotic derives_from confers_resistance_to_antibiotic caspofungin echinocandin-resistant fungal cytochrome P450 enzyme antifungal susceptible Cyp51 enzyme Aspergillus fumigatus Cyp51A with mutations conferring resistance to caspofungin antibiotic_resistance ARO:3009557 Echinocandins inhibit beta-1,3-D-glucan synthase, disrupting fungal cell wall biosynthesis rather than sterol production. Although resistance to echinocandins is classically driven by mutations in the FKS genes, alterations in sterol biosynthesis pathways, including mutations in Cyp51, have been shown in some fungi to indirectly influence echinocandin susceptibility. Cyp51 mutations can modify membrane sterol composition and cell envelope architecture, affecting cell wall stress responses and compensatory signaling pathways. These secondary effects may reduce echinocandin efficacy and contribute to tolerance or reduced susceptibility, even though Cyp51 is not the direct molecular target of echinocandins.