Type II fatty acid synthesis (FASII) is essential to bacterial cell viability. The significant differences between bacteria and humans in organization, structure of enzymes, and the role played by fatty acids make this pathway an attractive target for antibacterial drug discovery (refs. 1,2). Two marketed antibacterial agents that target the FabI enzyme are triclosan (antiseptic) and isoniazid (an anti-Mycobacterium tuberculosis agent) (refs 3,4). Two natural products, cerulenin (ref. 5) and thiolactomycin (ref. 6) which selectively inhibit the condensation enzymes FabH and FabF/B, were discovered more than two decades ago. New screening efforts and chemical modifications of existing compounds have been attempted to identify more selective and potent inhibitors. To determine the selectivity of the inhibitors identified during screening efforts we developed gel-elongation assay using crude bacterial lysate directly to determine the target specificities of fatty acid synthesis inhibitors (refs. 7,8).