Synthetically-derived S,S-heterodisubstituted disulfides that exhibit potent in vitro antibacterial activity against a variety of bacteria, including Staphylococcus aureus, methicillin-resistant Staphylococcus aureus and Francisella tularensis. The present invention provides compounds, methods and compositions effective to treat microbial/bacterial infections, and, especially, infections arising from bacteria which have developed resistance to conventional antibiotics.