Disinfectant resistance mechanisms, cross-resistance, and co-resistance

Six major classes of disinfectants and sanitizers are iodophors, quaternary ammonium compounds (QAC), peroxides, phenols, chlorine, and glutaraldehyde. Bacterial resistance to each of these classes has been reported in literature, and anecdotal reports within the biocide industry are common. Resistance to disinfectants and sanitizers can have significant impact on human health as well as serious economic consequences. The mechanisms associated with resistance have received uneven attention; in the case of resistance to QAC disinfectants and peroxides our knowledge extends to the genetic level while for the other classes the literature consists of largely phenomenological descriptions of its occurrence. Even less is known about the frequency with which resistance develops and the impact of environmental factors on resistance development. Amongst environmental factors the role of biofilms is of interest particularly as they relate to the exposure of bacteria to sublethal concentrations of disinfectant. In industrial systems the selective pressure from preservative usage has been postulated to play a role in disinfectant resistance development through mechanisms of cross-resistance; some isothiazolone and formaldehyde resistant bacteria are cross-resistant to QAC and/or peroxide disinfectants. Mechanism-based cross-resistance of disinfectant-resistant bacteria to antibiotics is of great interest recently, but remains a ripe area for systematic investigation. Co-resistance of disinfectant-resistant bacteria to antibiotics occurs as a result of QAC resistance genes being located on transmissible plasmids and within conserved regions of integrons, each of which has been shown to carry multiple antibiotic resistance genes. (C) 2003 Elsevier Science Ltd. All rights reserved.