plasmids)duringthe evolutionof the organism. A general overviewof relevant
disinfectantsand theirmodeof actionis given in Table4.1.
Thepossible modeof actionsof the applied disinfectingtreatmentsand
pathogenresponseas discussed in the previoussection are discussedbelow.
4.4.1 Targetareaof disinfectant
∑ Cell membrane and its outerlayers, breakingdownresults in quickcell death/
inactivation of the microorganism(Todar,2001).
∑ Damage to enzymes + importantmetabolic processes; someheavymetals
(e.g.copper,silver, mercury)act as poisons to enzymes. Addedas saltsor
organiccombinationstheybind to SH groupsof enzymes and causechanges
in the structure(tertiaryand quaternary)of these proteins (Schlegel, 1993).
∑ Affecting the synthesisof proteins in the targetorganism results in growth
prohibition (Todar, 2001;Schlegel, 1993).
∑ Inhibition of DNAsynthesis or breakageof the DNAstrands, resultingin the
blockageof cell growth (McDonnell and Russell,1999).
4.4.2 Pathogen response
Addingdisinfectantswillresult in increasedstresson the bacteriaand their
metabolism.In principle theyhavethreewaysof responding to disinfectants:
∑ alteration of the target;
∑ reductionof targetaccess;
∑ inactivation of the disinfectant.
As disinfectants have a broadspectrumof activity, it is not likely that the
alteration of the targetwill work.The two other mechanisms seemto be possible
and a combinationof resistancemechanisms is alsoone of the possibilities
(Chapman, 1998).The fact that microorganismsshowthis kindof behaviouris
causedby eitherintrinsic or acquired resistance (Russell, 1995;McDonnelland
Russell,1999).
4.4.3 Intrinsic resistance
Thistype of resistanceis definedas a naturalchromosomally controlledproperty
of a bacterial cell to circumventthe action of a disinfectant. It is demonstrated
especially by Gram-negative bacteria and bacterialspores (Russell, 1991;
McDonnell and Russell, 1999). Bacterial spores, the genera Bacillus and
Clostridiumin particular,are the mostresistant, e.gCl. perfringensandB.
cereus(Russell, 1995).The exactmechanismof sporicidalactionis not fully
understood;however, as the prime targetarea of biocides lies withinthe sporeit
is expectedthat,owingto the differentlayersof the spore, the penetrationof
biocides is limited.
Pathogen resistanceto sanitisers 83