Modeof action
The general modeof actionfor inactivationof microorganismsby alcohols is by
denaturation of proteins(Schlegel, 1993),withthe primarysite of actionbeing
the cell (plasma)membrane. As a result of deteriorationof the plasmamembrane,
the cell wall starts to leak essentialcell components suchas ions (Ca2+) and low
molecular weightsolutessuchas peptides and aminoacids. Therefore,the mode
of actionand its effect on the metabolismof the microorganism depends very
muchon the concentration.Mouldsand actinomycetesare mostsusceptible to
alcohols and are inhibited at 4% (v/v) whereas mostbacteria can still growat
theseconcentrations(Kalathenosand Russell, 2003).Applicationof 5.5%(v/v)
showsa bacteriostatic effectonE. coli, but in orderto kill this microorganism
concentrationsof 22.2%or higherare necessary (Allerberger and Dierich,1988).
Yeasts are able to growat higheralcoholconcentrations (8±12%v/v),whichis
not surprisingsincetheyare responsiblefor the production of beerand wine
(Saccharomycescerevisiae). Sporesare affectedby ethanol.Setlowand co-
workers (2002)showedthat the sporecoat can be permeabilized. Consequently,
ethanolin combination with other components or with high temperature (> 65 ÎC)
is moreeffectivethanethanolitself in activating spores.
4.2.5 Aldehydes
Twoaldehydecompoundsare mainlyusedfor disinfecting,glutaraldehydeand
formaldehyde.Aldehydes are activeagainsta wide rangeof bacteria,viruses,
mouldsand spores, are easilyremovedfromsurfaces and are (bio)degradable
(Mohr and Duggal, 1997).However,the activity of aldehydesis veryeasily
influencedby remaining (protein)fouling, whichnecessitatessufficient cleaning
priorto disinfecting. Froma toxicological pointof view,aldehydes do not cause
problems for humans whenusedwithinthe prescribedconcentrations(Mohr and
Duggal, 1997).On the other hand,it is possible that formaldehydecan have
mutagenic effects(McDonnell and Russell,1999).
Modeof action
The modeof actionof glutaraldehydeinvolvesa strongassociationwiththe
outerlayersof bacterial cells (Denyerand Stewart, 1998; McDonnelland
Russell,1999).The cell's chemical reactionwithglutaraldehyderesults in
metabolic and replicative inhibition(Denyerand Stewart, 1998).Theway
formaldehyde reacts is most probably the same. Concerning processing
conditions, an alkalienvironment is morefavourablethanan acid environment
as morereactive siteswill be formedon the cell surface. Applied concentrations
varybetween 0.08and 1.6%(w/w)for inactivatingE. coli. For a sporicidal
effect,a solution of 2% is normally sufficient.
4.2.6 Bisphenols
Bisphenolsare hydroxyhalogenatedderivativesof diphenylmethane,diphenyl
etherand diphenylsulphide,and are activeagainstbacteria,fungi and algae.
Pathogen resistanceto sanitisers 75