[Epidemiology and reasons for microbial resistance to biocides]

In the last years the significance of microbial resistance to biocides like toxic heavy metal ions, aldehydes, phenoles, and cationic surface active agents has increased. However the genetical and functional mechanisms of the resistance to most of these compounds are still unknown. Till now it was possible to demonstrate a plasmid resistance in only some bacterial strains which were resistant to heavy metal ions, hexachlorophene, formaldehyde, benzalkoniumchloride, and chlorhexidine. In mercuric resistant Staphylococcus aureus and formaldehyde resistant E. coli strains the resistance genes are now well characterized. These strains are able to produce enzymes which degradade the disinfectant. The resistance to cationic surface active agents seems to depend on a modification of the bacterial cell wall. This is concluded from former investigations with benzalkoniumchloride resistant Pseudomonas strains, where it was possible to demonstrate different lipid contents in the cell wall from resistant and sensitive strains.