A triclosan-resistant bacterial enzyme

Antibacterial household products: cause for concern

The recent entry of products containing antibacterial agents into healthy households has escalated from a few dozen products in the mid-1990s to more than 700 today. Antibacterial products were developed and have been successfully used to prevent transmission of disease-causing microorganisms among patients, particularly in hospitals. They are now being added to products used in healthy households, even though an added health benefit has not been demonstrated. Scientists are concerned that the antibacterial agents will select bacteria resistant to them and cross-resistant to antibiotics. Moreover, if they alter a person's microflora, they may negatively affect the normal maturation of the T helper cell response of the immune system to commensal flora antigens; this change could lead to a greater chance of allergies in children. As with antibiotics, prudent use of these products is urged. Their designated purpose is to protect vulnerable patients.

The enoyl-[acyl-carrier-protein] reductases FabI and FabL from Bacillus subtilis

Enoyl-[acyl-carrier-protein] (ACP) reductase is a key enzyme in type II fatty-acid synthases that catalyzes the last step in each elongation cycle. The FabI component of Bacillus subtilis (bsFabI) was identified in the genomic data base by homology to the Escherichia coli protein. bsFabI was cloned and purified and exhibited properties similar to those of E. coli FabI, including a marked preference for NADH over NADPH as a cofactor. Overexpression of the B. subtilis fabI gene complemented the temperature-sensitive growth phenotype of an E. coli fabI mutant. Triclosan was a slow-binding inhibitor of bsFabI and formed a stable bsFabI.NAD(+). triclosan ternary complex. Analysis of the B. subtilis genomic data base revealed a second open reading frame (ygaA) that was predicted to encode a protein with a relatively low overall similarity to FabI, but contained the Tyr-Xaa(6)-Lys enoyl-ACP reductase catalytic architecture. The purified YgaA protein catalyzed the NADPH-dependent reduction of trans-2-enoyl thioesters of both N-acetylcysteamine and ACP. YgaA was reversibly inhibited by triclosan, but did not form the stable ternary complex characteristic of the FabI proteins. Expression of YgaA complemented the fabI(ts) defect in E. coli and conferred complete triclosan resistance. Single knockouts of the ygaA or fabI gene in B. subtilis were viable, but double knockouts were not obtained. The fabI knockout was as sensitive as the wild-type strain to triclosan, whereas the ygaA knockout was 250-fold more sensitive to the drug. YgaA was renamed FabL to denote the discovery of a new family of proteins that carry out the enoyl-ACP reductase step in type II fatty-acid synthases.