FIG 3.

CAS induces modification of β-glucan synthase in RG101 and several clinical isolates. Sensitivity of partially purified glucan synthase to different echinocandins was examined in vitro after isolating the enzyme from RG101 grown in different drug conditions. (A) Dose-dependent insensitivity of RG101 glucan synthase to CAS induced by CAS during mycelial growth of RG101. The IC₅₀ of glucan synthase for RG101 grown in the absence of CAS [IC₅₀ (no CAS)] was ∼0.01 ng/ml and for RG101 grown at 4 μg/ml CAS [IC₅₀ (4 μg/ml CAS)] was high at >10,000 ng/ml. Previous exposure to CAS in RG101 culture induced insensitivity to CAS at the enzyme level in a dose-dependent fashion. (B) Previous exposure to CAS in culture induced insensitivity to micafungin at the enzyme level [IC₅₀ (no CAS), <0.01 ng/ml; IC₅₀ (4 μg/ml CAS), >10,000 ng/ml], indicating potential CAS-induced cross-resistance in cells. (C to E) Enzyme profiles similar to those seen with CAS were observed in clinical isolates 117 (C), 2770 (D), and 32458 (E). IC₅₀ values for the three clinical isolates are as follows: for isolate 117, IC₅₀ (no CAS) = ∼0.01 ng/ml and IC₅₀ (4 μg/ml CAS) = >10,000 ng/ml; for isolate 2770, IC₅₀ (no CAS) = ∼0.01 ng/ml and IC₅₀ (4 μg/ml CAS) = >10,000 ng/ml; for isolate 32458, IC₅₀ (no CAS) = ∼10 ng/ml and IC₅₀ (4 μg/ml CAS) = ∼5,000 ng/ml.