Transcriptional profiling reveals that daptomycin induces the Staphylococcus aureus cell wall stress stimulon and genes responsive to membrane depolarization

Abstract

Daptomycin is a lipopeptide antibiotic that has recently been approved for treatment of gram-positive bacterial infections. The mode of action of daptomycin is not yet entirely clear. To further understand the mechanism transcriptomic analysis of changes in gene expression in daptomycin-treated Staphylococcus aureus was carried out. The expression profile indicated that cell wall stress stimulon member genes (B. J. Wilkinson, A. Muthaiyan, and R. K. Jayaswal, Curr. Med. Chem. Anti-Infect. Agents 4:259-276, 2005) were significantly induced by daptomycin and by the cell wall-active antibiotics vancomycin and oxacillin. Comparison of the daptomycin response of a two-component cell wall stress stimulon regulator VraSR mutant, S. aureus KVR, to its parent N315 showed diminished expression of the cell wall stress stimulon in the mutant. Daptomycin has been proposed to cause membrane depolarization, and the transcriptional responses to carbonyl cyanide m-chlorophenylhydrazone (CCCP) and nisin were determined. Transcriptional profiles of the responses to these antimicrobial agents showed significantly different patterns compared to those of the cell wall-active antibiotics, including little or no induction of the cell wall stress stimulon. However, there were a significant number of genes induced by both CCCP and daptomycin that were not induced by oxacillin or vancomycin, so the daptomycin transcriptome probably reflected a membrane depolarizing activity of this antimicrobial also. The results indicate that inhibition of peptidoglycan biosynthesis, either directly or indirectly, and membrane depolarization are parts of the mode of action of daptomycin.

FIG. 1.

GICs of the antimicrobial agents for S. aureus strain ATCC 29213. (a) Daptomycin. ♦, control; ▪, 1 μg ml⁻¹; ▴, 5 μg ml⁻¹; ×, 10 μg ml⁻¹. (b) Vancomycin. ♦, control; ▪, 2 μg ml⁻¹; ▴, 4 μg ml⁻¹; ×, 10 μg ml⁻¹. (c) CCCP. ♦, control; ▪, 2 μg ml⁻¹; ▴, 4 μg ml⁻¹; ×, 10 μg ml⁻¹. (d) Nisin. ♦, control; ▪, 7.5 μg ml⁻¹; ▴, 15 μg ml⁻¹; ×, 20 μg ml⁻¹; *, 25 μg ml⁻¹.

FIG. 2.

Daptomycin GICs for S. aureus strains N315 (a) and KVR (b). (a) ♦, control; ▪, 1 μg ml⁻¹; ▴, 4 μg ml⁻¹; ×, 10 μg ml⁻¹. (b) ♦, control; ▪, 0.8 μg ml⁻¹; ▴, 2 μg ml⁻¹; ×, 4 μg ml⁻¹.

FIG. 3.

Comparison of daptomycin-induced genes in S. aureus ATCC 29213 and S. aureus N315 vraSR mutant KVR. †, genes reported by Kuroda et al. (31).

FIG. 4.

Venn diagram analysis of genes induced in response to daptomycin (Dap) and cell wall-active antibiotics vancomycin (Van) and oxacillin (Oxa) (+, up-regulated genes; −, down-regulated genes).