The subject invention pertains to a modified lantibiotic containing an intact cysteine at the C-terminus, particularly, a cysteine that is not decarboxylated and that contains a free carboxyl group. Derivatives of the modified lantibiotic comprising a moiety conjugated to the carboxyl group of the terminal cysteine are also provided. A bacterium that produces a modified lantibiotic having an intact cysteine at the C-terminus are also provided, wherein the bacterium is genetically modified to inactivate a gene that encodes a decarboxylase enzyme that decarboxylates the cysteine at the C-terminus of a precursor lantibiotic. Methods of producing a modified lantibiotic having an intact cysteine at the C-terminus by culturing a bacterium that synthesizes the modified lantibiotic and purifying the lantibiotic are also provided. Mutants of lantibiotics, particularly, mutacin 1140 having higher anti-bacterial activity or higher bacterial expression compared to mutacin 1140 are also provided.