Modeof action
In principle chlorhexidine attacksthe outercell layerbut not sufficientlyto
induce lysisor cell death.However, aftercrossing the cell wallit damagesthe
cytoplasmicmembrane (bacteria)or plasmamembrane(yeast)(McDonnelland
Russell,1999).Polymericbiguanide appearsto havea non-specific modeof
attack againstcell membranesresultingin quickcell death.
Summary
The differenteffectiveconcentrationsfor the biocides are summarised in Table
4.3.It is obvious that,depending on the typeof application or type and
metabolic stateof the microorganism,the proper disinfectantmustbe chosen.
4.3 Strategiesfor optimisationof cleaning and disinfection
Resistancedevelopment as a resultof cleaningand disinfectionis not (yet)a
matter of majorconcernfor the foodindustry. Howeverthe foodindustry (and
also the pharmaceuticalindustry) has to realise that the currentprocessesof
cleaningand disinfecting needto be carried out properly in orderto avoid
development of resistance. Even a short-term exposure to sub-lethal
concentrationsof QACs causescellularchanges ofListeria monocytogenes
(Lunde¬net al., 2003).In addition, recirculationof product in the processchain
(re-work)impliesa possible risk as (remaining)microorganismsare exposed a
second time to a cleaning and disinfecting step. This might induce the
developmentof resistantmutantsof the spoilagemicroorganisms.
For the application of cleaningand disinfectingagentsthe followingissues
are important:
∑ use of appropriateproduct;
∑ applicationof correctprocessingconditions;
∑ influence of neutralisingcomponents;
∑ monitoring.
4.3.1 Use of the appropriateproduct
Application of the right typeof agent is importantto achieve the desired
chemical effect. Withrespect to disinfectants it is necessarythat a productwith
the properspectrum of activity is chosen. For example,to inactivate spores the
applicationof alcoholsor QACs is uselessas thoseagentsare not sporicidal
(Russell, 1990).Anotherpointis that somesolutions(e.g.chlorine solutions)act
veryaggressively towards metalsurfacesand polymerseals.Thisresults in
corrosionof the materials providing bacteriawithplaceswheretheyare able to
survive cleaning and disinfecting procedures (Kraemer,1998).
78 Handbookof hygiene controlin the foodindustry