PHENOMENA OF BIOCIDE RESISTANCE IN MICROORGANISMS

Intrinsic tolerance of microorganisms to different biocides varies con siderably and may be clustered according to its biological variance in 3 groups: 1. The variance is very small, i.e. the majority (> 90%) of strains of a certain species has the same m.i.c. 2. The tolerance is binomially distributed with variance factors between 5-50.3. The toler ance is bimodally distributed, i.e. there are 2 m.i.c.-maxima. There i s a problem to define exactly where the natural variance of tolerance should end and a resistance begins. There is another problem to separa te true resistance from pseudo-resistance which is mainly caused by mi stakes in the application of disinfectants. True resistance still is a rather rare event while pseudo-resistance is frequent. Resistance may be acquired under natural or practical conditions or may be artificia lly increased under laboratory conditions. Adaptation is an intermedia te resistance caused by the physiological conditions of the biotope. A daptive resistance is lost rapidly as soon as these physiological cond itions change. Known mechanisms of true resistance are: 1. Exclusion o f the active agent from the cellular loci of lethal destruction.2. Sec retion or enzymatic detoxification of the active agents. Bacterial res istance to biocides is genetically determined by plasmids or by the ch romosome. It has also been demonstrated by in vitro experiments that f ormaldehyde resistance is transferable. QAC-resistance plasmids in sta phylococcal strains isolated from meat processing industry could also be found in Staphylococci from other food branches. This gives first e vidence for the possibility of an epidemiological development of bioci de resistance. (C) 1998 Elsevier Science Ltd. All rights reserved.