Inhibitory Effects on Staphylococcus aureus Sortase A by Aesculus sp. Extracts and Their Toxicity Evaluation

Abstract

A promising strategy for combating bacterial infections involves the development of agents that disarm the virulence factors of pathogenic bacteria, thereby reducing their pathogenicity without inducing direct lethality. Sortase A, a crucial enzyme responsible for anchoring virulence factors to the cell surface of several pathogenic bacteria, has emerged as a possible target for antivirulence strategies. A series of hippocastanum species (Aesculus pavia, A. parviflora, Aesculus x carnea, and A. hippocastanum) were used to prepare ethanol- and water-based extracts for assessing their effect on Staphylococcus aureus sortase A. The extracts were characterized through HPLC analysis, and their polyphenols content was determined using the Folin-Ciocalteu method. The specific toxicity profile was evaluated in Daphnia magna using the median lethal concentration (LC₅₀) and against the fibroblast MRHF cell line. The half maximal inhibitory concentration (IC₅₀) values on sortase A, determined after 30 min of incubation, ranged from 82.70 to 304.31 µg/mL, with the A. pavia water extract exhibiting the highest inhibitory effect. The assessment of the A. pavia water extract on human fibroblasts revealed no significant signs of toxicity, even at a concentration of 500 µg/mL. This reduced toxicity was further validated through the Daphnia assay. These findings highlight the low toxicity and the potential of this extract as a promising source of future development of bacteria antivirulence solutions.

Keywords: Daphnia magna assay; MRHF cells; antivirulence agents; bottlebrush buckeye; horse chestnut; polyphenols; red buckeye.

Figure 1

The inhibition (I%) of SrtA activity measured after 30 and 60 min of exposure to the extracts: (a) PVw—aqueous extract from Aesculus pavia leaves; (b) PVm—50% ethanolic extract from the leaves of A. pavia; (c) PVe—96% ethanolic extract of A. pavia leaves; (d) PRw—aqueous extract of Aesculus parviflora leaves; (e) HCe—96% ethanolic extract from leaves of Aesculus hippocastanum; (f) CRm—50% ethanolic extract from leaves of Aesculus x carnea.

Figure 2

Cytotoxicity of 6 samples tested against MRHF cells. Cells were treated for 48 h. Melphalan was used as the positive control (15, 30, and 60 µM). Error bars indicate standard deviation of quadruplicate values. * p < 0.05; ** p < 0.01; *** p < 0.001 compared to untreated control cells.