Triclosan has activity against many, but not all, types of Gram-positive and Gram-negative bacteria. It is bacteriostatic at low concentrations, but higher concentrations are bactericidal. Pseudomonas aeruginosa is highly resistant, whereas methicillin-resistant Staphylococcus aureus strains are inhibited over a range of approximately 0.1-2 mg/L. Triclosan shows significant activity against some mycobacteria, but is not sporicidal. Its growth-inhibitory properties result from an inhibition of enoyl reductase, FabI. Membrane-destabilizing effects are likely to be responsible for bacterial inactivation by higher concentrations. Resistance can arise from mutations in, and/or overproduction of, FabI, impermeability or efflux. Whilst triclosan resistance in laboratory experiments may be associated with changes in antibiotic susceptibility, comprehensive environmental surveys have not demonstrated any association between triclosan usage and antibiotic resistance. Triclosan has several important uses, and the future aim must be to retain these applications whilst eliminating the more frivolous and unnecessary ones.