Tarocin A1 is an oxazolidinone which inhibits TarO, the first enzyme in teichoic acid synthesis. Tarocin A1 has an IC50 value of 40 nM in a biochemical TarO assay. Tarocin A does not inhibit bacterial growth alone, and exhibits no cytotoxicity against HeLa cells, but it has potent bactericidal syergism with broad spectrum β-lactams, and may restore the clinical efficacy of existing β-lactam antibiotics.