Interception of Epoxide ring to quorum sensing system in Enterococcus faecalis and Staphylococcus aureus

Abstract

Quorum sensing inhibitor (QSI) has been attracting attention as anti-virulence agent which disarms pathogens of their virulence rather than killing them. QSI marking cyclic peptide-mediated QS in Gram-positive bacteria is an effective tool to overcome the crisis of antibiotic-dependent chemotherapy due to the emergence of drug resistance strain, e.g., methicillin resistant Staphylococcus aureus (MRSA) and Vancomycin resistant Enterococci (VRE). From a semi-large-scale screening thus far carried out, two Epoxide compounds, Ambuic acid and Synerazol, have been found to efficiently block agr and fsr QS systems, suggesting that the Epoxide group is involved in the mode of action of these QSIs. To address this notion, known natural Epoxide compounds, Cerulenin and Fosfomycin were examined for QSI activity for the agr and fsr systems in addition to in silico and SAR studies. As a result, most of investigated Epoxide containing antibiotics correlatively interfere with QSI activity for the agr and fsr systems under sublethal concentrations.

Keywords: Enterococcus faecalis; Quorum sensing; Staphylococcus aureus; agr, fsr, Epoxide ring ADMET and Docking Studies..

Fig. 1

A: The chemical structure Cerulenin. B: Effect of cerulenin on E. faecalis OG1RF growth and gelatinase production. E. faecalis was grown in the presence or absence of cerulenin at the designated concentrations; the density of culture measured at the OD₆₂₀ (closed square), and gelatinase activity was measured at OD₅₄₀ (open square), the test was performed, and data represented as an average of triplicate experiments, ± standard deviation.

Fig. 2

A: The chemical structure of fosfomycin. B: Effect of fosfomycin on E. faecalis OG1RF growth and gelatinase production. E. faecalis in the presence or absence of fosfomycin at the designated concentrations; the density of culture measured at the OD₆₂₀ (closed square), while gelatinase activity at OD₅₄₀ (open square), the test was performed and data represented as an average of triplicate experiments, ± standard deviation.

Fig. 3

A: The chemical structure 1,2-epoxybutane. B: Effect of 1, 2-epoxybutane on E. faecalis OG1RF growth and gelatinase production. E. faecalis was grown in the presence or absence of 1, 2-epoxybutane at the designated concentrations; the density of culture measured at the OD₆₂₀ (closed square), and gelatinase activity was measured at OD₅₄₀ (open square), the test was performed, and data represented as an average of triplicate experiments, ± standard deviation.

Fig. 4

A: The chemical structure 1, 2-epoxyethylbenzene [49]. B: Effect of 1, 2-epoxyethylbenzene on E. faecalis OG1RF growth and gelatinase production. E. faecalis was grown for 5 h in the presence or absence of 1, 2-epoxyethylbenzene at the designated concentrations; the density of culture measured at the OD₆₂₀ (closed square), and gelatinase activity was measured at OD₅₄₀ (open square), the test was performed, and data represented as an average of triplicate experiments, ± standard deviation.

Fig. 5

A: The chemical structure of 2,3-epoxypropyl phenyl ether [50]. B: Effect of 2, 3-epoxypropyl phenyl ether on E. faecalis OG1RF growth and gelatinase production. E. faecalis was grown for 5 h in the presence or absence of 2, 3-epoxypropyl phenyl ether at the designated concentrations; the density of culture measured at the OD₆₂₀ (closed square), and gelatinase activity was measured at OD₅₄₀ (open square), the test was performed, and data represented as an average of triplicate experiments, ± standard deviation.

Fig. 6

A: The chemical structure of glycidyl methacrylate [49]. B: Effect of glycidyl methacrylate on E. faecalis OG1RF growth and gelatinase production. E. faecalis was grown for 5 h in the presence or absence of glycidyl methacrylate at the designated concentrations; the density of culture measured at the OD₆₂₀ (closed square), and gelatinase activity was measured at OD₅₄₀ (open square), the test was performed, and data represented as an average of triplicate experiments, ± standard deviation.

Fig. 7

Effect of IC₅₀ for QSIs on E. faecalis OU510 gelatinase production. This strain was induced by GBAP. E. faecalis OU510 was grown for 5 h in the presence of the designated concentrations of GBAP without QSIs (closed triangle with dashed line) or with 0.4 µM synerazol (open squares), 1.8 µM cerulenin (closed circle), 6 µM styrene oxide (closed square), and 4 µM 2, 3-epoxypropyl phenyl ether (open triangles). the test was performed, and data represented as an average of triplicate experiments, ± standard deviation.

Fig. 8

Effect of compounds on S. aureus 8325–4(pSB2035) agr expression in. The dual reporter strain grew in the presence or absence of various concentrations of compounds. After 7 h, the OD₆₂₀, fluorescence at 490 nm and 470 nm and chemiluminescence of the culture were measured. A: 1, 2-epoxyethylbenzene, B: 2, 3-epoxypropyl phenyl ether, C: glycidyl methacrylate.

Fig. 9

The two dimensional (1) and three-dimensional (2) interacting mode of A: Cerulenin B: Fosfomycin, C: Ambuic acid in the active region of AgrA (PDB code: 3BS1).