water) (Fraise, 2004a). In addition, preservation now includes medicines,
pharmaceutical and cosmeticproducts, but also paint,wood, variousplasticand
textiles, and is usedin the petroleumand construction industries.The choice of
preservatives has to be balanced between antimicrobial efficacy (now
increasinglymicrobicidalactivity) and low toxicity.
38.2.2 Factors influencingbiocidalactivity
Severalfactorscan affectthe antimicrobialefficacyof chemicalbiocides(Table
38.3).Thesefactorshave usuallybeen wellcharacterisedfor manyof these
compounds(Russell,2004).However,theirpracticalsignificancefor the end-
productand its usageis rarelydiscussed.Failureof a disinfection/sanitisation
processoftenreflectsthe non-respector lackof understandingof thesefactors.
Hence,it is importantto combinethe use of a suitableantimicrobialproduct/
formulationfor a specifictask withthe trainingof the end user.Sincecompliance
to the manufacturer'sinstructionsis particularlyimportant,the efficacyof an
Table38.3 Factorsinfluencingthe activityof biocides
Factors Comments
Concentration The maincausefor failureof disinfection.Dilutioncan
inactivatebiocides,notablythosewitha highconcentration
exponent.
Contacttime Non-respectof, or poorcompliancewith,contacttimecan result
in the survivalof microorganisms.Contacttimeneedsto be
adaptedto the conditionof usage.
Organicload Particularlyimportantin the foodindustry,and in the clinical
contextwithbloodspillage.Can severelyreducethe
antimicrobialefficacyof biocides.
Temperature Couldbe an issuewhenbiocidesare usedin coldconditions;
e.g. coldroom,chilledfoodproduction,or withthe efficacyof
preservatives(i.e. productskeptat a low temperature).
pH Can affectboththe microorganismsand the agents,especiallyif
it is an acidor a base.
Microorganisms
Type Microorganismsvaryin susceptibilityto biocides,prionsand
sporesbeingthe mostresistantto disinfection.
Number Heavymicrobialcontaminationis moredifficultto disinfect/
sanitise.
Phenotype Microorganismsgrownas biofilms,or witha low metabolism
are moreresistantto antimicrobialsthanplanktonicgrown
microorganismsand microorganismsgrownon `rich'media.
Relativehumidity Particularlyimportantfor gaseousdisinfectants.Pre-
humidificationaffectsthe hydrationstateof microorganisms.
Neutralisation/ Can inactivatecompletelyor partiallythe activityof a biocide.
incompatibility Knowledgeof the productsis important.
Testingthe effectivenessof disinfectants and sanitisers 645