Mechanisms of bacterial insusceptibility to biocides.

Bacterial insusceptibility to biocides is of two types, intrinsic and acquired. Intrinsic insusceptibility is a natural property of an organism and is shown by bacterial spores, mycobacteria, and gram-negative bacilli. Cellular impermeability is a major factor, and in some cases active efflux pumps play an important role. A special example is that of phenotypic (physiological) adaptation to intrinsic resistance found in bacteria present in biofilms. Acquired resistance arises through mutation or via the acquisition of plasmids or transposons; efflux of biocide is a major mechanism, although plasmid-mediated inactivation has also been shown to occur. An additional aspect that must be considered is the stringent response elicited in bacteria on exposure to inimical agencies. There is a possible linkage between certain biocides and antibiotic resistance under experimental conditions.