Biocide abuse and antimicrobial resistance--a cause for concern?

The term biocide includes disinfectants, antiseptics and preservatives. It does not include antibiotics, which, in spite of being biocides in the strictest sense, tend to be categorized separately. In recent years there has been a trend towards use of biocides in the home environment. These products have been marketed for decontamination of food preparation surfaces (e.g. Dettox), areas perceived to be microbially contaminated (e.g. toilets) and general improvement of cleanliness in the home. A product called Microban is a biocide (triclosan) that is incorporated into chopping boards, knife handles and Wellington boots. Other companies manufacture biocide-impregnated paint (Biocote) and toilet seats. Several workers have suggested that widespread use of biocides may impact on the prevalence of antibiotic-resistant microorganisms. What is the evidence that biocide use selects for antibiotic resistance? Biocide resistance was first recognized nearly 70 years ago by Heathman et al. 1 who identified chlorine resistance in Salmonella typhi, and antibiotic resistance was identified shortly after the availability of penicillin, but links between the two have only been recognized more recently. It is remarkable that there is a large amount of data on antibiotic resistance, with journals such as this one devoting many pages to papers describing resistance mechanisms and other journals devoted solely to the topic of antibiotic resistance. Yet there is a comparatively small number of workers worldwide who are investigating the mechanics of biocide resistance. Because biocides tend to act concurrently on multiple sites within the microorganism, resistance is often mediated by non-specific means. Efflux pumps have the potential to act on a range of chemically dissimilar compounds and have been implicated in both biocide-and antibiotic-resistant bacteria. Cell wall changes may also play a role in the observed cross-resistance between biocides and antibiotics , probably by reducing permeability. Microbial changes that result in resistance to biocides and antibiotics should therefore cause concern. However, of equal significance , is the possibility of genetic linkage between genes for biocide resistance and those for antibiotic resistance. McMurry & Levy 2 reported in 1998 that mutations in the enoyl reductase gene (fab1) of Escherichia coli were associated with resistance to triclosan. This work suggested that Fab1 is the target for triclosan but failed to demonstrate any significant reduction in susceptibility to antibiotics in strains with fab1 mutations. However, the same workers have demonstrated that Inh1 (the mycobacterial analogue of the Fab1 protein) is a common target for triclosan and isoniazid …