Antibacterial Activity and Membrane-Targeting Mechanism of Aloe-Emodin Against Staphylococcus epidermidis

The emergence of multidrug-resistant Staphylococcus epidermidis (S. epidermidis) dwarfs the current antibiotic development and calls for the discovery of new antibacterial agents. Aloe-emodin is a plant-derived compound that holds promise to battle against these strains. This work reports the antimicrobial activity of aloe-emodin against S. epidermidis and other Gram-positive pathogenic species, manifesting minimum inhibitory concentrations (MICs) and minimum bactericidal concentration (MBCs) around 4-32 and 32-128 μg/mL, respectively. For Gram-negative bacteria tested, the MICs and MBCs of aloe-emodin were 128-256 and above 1024 μg/mL, respectively. Aloe-emodin at the MBC for 4 h eradicated 96.9% of S. epidermidis cells. Aloe-emodin treatment led to deformities in the morphology of S. epidermidis cells and the destroy of the selective permeability of the cell membranes. Analysis of the transcriptional profiles of aloe-emodin-treated cells revealed changes of genes involved in sulfur metabolism, L-lysine and peptidoglycan biosynthesis, and biofilm formation. Aloe-emodin therefore can safely control Gram-positive bacterial infections and proves to target the bacterial outer membrane.