Targeting Staphylococcus aureus quorum sensing with nonpeptidic small molecule inhibitors

Abstract

A series of 3-oxo-C12-HSL, tetramic acid, and tetronic acid analogues were synthesized to gain insights into the structural requirements for quorum sensing inhibition in Staphylococcus aureus. Compounds active against agr were noncompetitive inhibitors of the autoinducing peptide (AIP) activated AgrC receptor, by altering the activation efficacy of the cognate AIP-1. They appeared to act as negative allosteric modulators and are exemplified by 3-tetradecanoyltetronic acid 17, which reduced nasal cell colonization and arthritis in a murine infection model.

Figure 1

(a) Iron-chelating properties of 5-HE-C10-TMA 5 and the C6-, C10-, and C12-TOAs 14, 15, 16 (at 50 μM) as determined using the CAS assay: positive control, desferrioxamine (10 μM); solvent control, MeCN. (b) 5-HE-TMAs and TOAs disturb the membrane dipole potential. Changes in dipole potential were determined using di-8-ANEPPS to measure the variation in the fluorescence ratio R(460/520) as a function of concentration. The binding profiles for 5-HE-C10-TMA 5 (■), C10-TOA 15 (▲), 5-HE-C12-TMA 7 (△), C12-TOA 16 (○), 5-HE-C14-TMA 8 (∗), and C14-TOA 17 (●) compared with 3-oxo-C₁₂-HSL 1 (▽) are shown.

Figure 2

3-Oxo-C₁₂-HSL 1, 5-HE-C10-TMA 5, and C12-TOA 16 do not compete with AIP-1 for cognate AgrC. Dose–response curves showing the inhibition of a blaZ-based agrP3 reporter by (a) 3-oxo-C₁₂-HSL 1, (b) 5-HE-C10-TMA 5, (c) C12-TOA 16, and (d) the competitive antagonist (Ala5)AIP-1.

Figure 3

Impact of C14-TOA 17 on adherence of S. aureus to desquamated human nasal epithelial cells and experimental infection. (a) Binding of S. aureus to squamous epithelial cells before or after treatment with 5-HE-C10-TMA 5 (A, 10 μM) or C14-TOA 17 (B, 1 μM). Counts represent the number of bacterial cells adhered to 100 nasal cells. Results are expressed as a mean of three experiments performed in duplicate. (b) Frequency of arthritis and (c) arthritic index of mice treated with 17 and challenged with S. aureus. White bars represent data from the control animals (PBS treated) and gray bars animals treated with 17 (10 mg/kg body weight). Data are presented as median (horizontal lines), interquartile ranges (bars), and ranges (error bars). An arthritic index was calculated by scoring all four limbs of each animal. Comparisons of groups for weight change and arthritis score were done by Mann–Whitney U test (∗, p < 0.05). Fischer exact probability test was used to calculate statistical differences in the frequency of arthritis.