The emergence of bacterial resistance to antimicrobial agents has caused increasing concern globally. the basis of bacterial resistance to antibiotics is well known, while the nonsusceptibility mechanisms of bacteria to biocides are less well understood. Recently, there is considerable interest in the problems associated with the development and spread of bacterial nonsusceptibility to biocides in order to understand the mechanisms of action and the bacterial nonsusceptibility mechanisms to biocides. Different groups of bacteria vary in their intrinsic nonsusceptibility to biocides, with bacterial spores being the most resistant, followed by mycobacteria, then Gram-negative organisms, with Gram-positive bacteria generally being the most susceptible. this intrinsic nonsusceptibility in some instances might be associated with constitutive degradative enzymes or due to active efflux pumps, but in reality cellular impermeability is considered as a major factor that plays an important role in the emergence of bacterial nonsusceptibility to biocides. Nonsusceptibility associated with biofilmforming bacterial cells can be considered an intrinsic nonsusceptibility mechanism resulting from physiological (phenotypic) adaptation cells.