Quorum sensing inhibitors of Staphylococcus aureus from Italian medicinal plants.

Morbidity and mortality estimates due to methi- cillin-resistant Staphylococcus aureus (MRSA) in- fections continue to rise. Therapeutic options are limited by antibiotic resistance. Anti-pathogenic compounds, which inhibit quorum sensing (QS) pathways, may be a useful alternative to antibiot- ics. Staphylococcal QS is encoded by the agr locus and is responsible for the production of δ-hemo- lysin. Quantification of δ-hemolysin found in cul- ture supernatants permits the analysis of agr ac- tivity at the translational rather than transcrip- tional level. We employed reversed phase high performance chromatographic (RP-HPLC) tech- niques to investigate the anti-QS activity of 168 extracts from 104 Italian plants through quantifi- cation of δ-hemolysin. Extracts from three medic- inal plants (Ballota nigra, Castanea sativa ,a nd Sambucus ebulus) exhibited a dose-dependent re- sponse in the production of δ-hemolysin, indicat- ing anti-QS activity in a pathogenic MRSA isolate.