Increases in SLT2 expression and chitin content are associated with incomplete killing of Candida glabrata by caspofungin

Abstract

Incomplete killing was observed for caspofungin against Candida glabrata, which was associated with increased SLT2 expression and elevated chitin content. In contrast, fungicidal activity and no chitin increase were observed in an isogenic Delta slt2 strain, suggesting a role for SLT2 and chitin production in the response of C. glabrata to caspofungin.

FIG. 1.

(A) In vitro XTT colorimetric assay. Percent absorbance (means ± standard deviations) for the parent C. glabrata strain, ATCC 200989 (•), and the corresponding Δslt2 (○) strain compared to results for the control are plotted on the y axis, and increasing concentrations of caspofungin (0 to 32 μg/ml) are plotted on the x axis. (B and C) Plots of log₁₀ CFU/ml (means ± standard deviations) versus time for the parent C. glabrata strain, ATCC 200989 (B), and the Δslt2 strain (C) at the following caspofungin concentrations: ▪ and □, control; ▴ and ▵, 0.125 μg/ml; ⧫ and ⋄, 1.0 μg/ml; • and ○, 16.0 μg/ml.

FIG. 2.

(A) Relative expression of SLT2 in parent strain C. glabrata ATCC 200989 (means ± standard deviations) following caspofungin exposure for 10 min (dark bars), 180 min (gray bars), or 12 h (white bars). (B) Relative expression of CHS3 in the parent C. glabrata strain, ATCC 200989 (dark bars), or the corresponding Δslt2 strain (gray bars) following caspofungin exposure for 180 min. Expression levels were normalized using ACT1 as the housekeeping gene. (C) Changes in chitin content (means ± standard deviations) compared to control levels in the parent C. glabrata strain, ATCC 200989 (dark bars), and the corresponding Δslt2 strain (gray bars) following exposure to 0.125, 1.0, or 16.0 μg/ml of caspofungin for 12 h.