Compounds that affect quorum sensing (QS) in Staphylococcus aureus and related Staphylococcus species (e.g., S. epidermidis). Compounds which modulate one or more of the four AgrC receptors of Staphylococcus species, particularly of Staphylococcus aureus. Modulation includes inhibition or activation of one or more of these four AgrC receptors. These compounds are useful for bacterial interference and are useful for treating bacterial infections, particularly staphylococcal infection. Treatment can include combination of one or more of the compounds of the invention in combination with one or more antibiotics.