Inhibition of the Staphylococcus aureus NADPH-dependent enoyl-acyl carrierprotein reductase by triclosan and hexachlorophene

Enoyl-acyl carrier protein reductase (FabI) plays a determinant role in com pleting cycles of elongation in type II fatty acid synthase systems and is an important target for antibacterial drugs. The FabI component of Staphylo coccus aureus (saFabI) was identified, and its properties were compared wit h Escherichia coli FabI (ecFabI), ecFabI and saFabI had similar specific ac tivities, and saFabI expression complemented the E, coli fabI (Ts) mutant, illustrating that the Gram-positive FabI was interchangeable with the Gram- negative FabI enzyme. However, ecFabI was specific for NADH, whereas saFabI exhibited specific and positive cooperative binding of NADPH, Triclosan an d hexachlorophene inhibited both ecFabI and saFabI, The triclosan-resistant ecFabI(G93V) protein was also refractory to hexachlorophene inhibition, il lustrating that both drugs bind at the FabI active site. Both the introduct ion of a plasmid expressing the safabI gene or a missense mutation in the c hromosomal safabI gene led to triclosan resistance in S, aureus; however, t hese strains did not exhibit cross-resistance to hexachlorophene, The repla cement of the ether linkage in triclosan by a carbon bridge in hexachloroph ene prevented the formation of a stable FabI-NAD(P)(+)-drug ternary complex . Thus, the formation of this ternary complex is a key determinant of the a ntibacterial activity of FabI inhibitors.