registration, applicationand use. These institutionshavedescribeda rangeof
protocolsavailablefor the testingof the antimicrobial activityof disinfectants
and sanitisers.
Suspensiontests
The mostcommonly usedtestingprotocols are basedon the suspensiontest. In
essence this test involvesmixinga microbialsuspension with a disinfectantfor a
set contacttimeand thenchecking for survivors aftera neutralisationor a
filtrationstep.Thesuspension test can be quantitativewhen the numberof
surviving bacteriais investigated,or qualitative (themost basicoption)for
whichan indication of microbial survivalis onlyrequired(i.e. a simple pass/fail
test).
Mostprimary testsare in the formof a qualitative suspension test during
whichthe potentialactivity of a biocide at a givenconcentrationand a set timeis
investigated. These preliminarytests are useful for a rapidevaluation of
antimicrobial activityof a seriesof concentrationsor contacttimes.There are
limitations to the suspension tests, notably when the result is assessed
qualitatively. Indeed, the growthand multiplicationof a lone survivorare
indistinguishable fromthe growth of part or the entirepopulation.Therefore the
antimicrobial effecton the growthand survivalof the entirepopulationcannot
be evaluated with these tests. Information on qualitative suspension test
protocolscan be foundprincipally fromGerman institutions(DVG,1988).The
additionof an enumerationstepis then highlybeneficial and most of the
suspensiontestsusedfor commercialand researchpurposesare nowquantita-
tive.Microorganisms are countedeitherby directagarplatingmethodor by
membrane filtration afterquenching/removingthe activity of the disinfectant/
sanitiser.The lethaleffect of the agent(ME)is calculated as follows:
MEàlog 10 NCˇlog 10 NDwhereNCis the numberof colony-formingunitsin the untreatedcontrol(s)and
NDthe numberof colony-formingunitscountedafterexposure to the biocide.
In Europe, the publication of the Europeanbactericidal suspensiontest (CEN,
1997a)addedmuch-neededstandardisationand supplantedvarious existing
tests, some of whichhavenow beenwithdrawn. Priorto that,the Dutchstandard
suspensiontest and quantitative suspension testspublished by AFNOR and
DGHM (Reybrouck,1980)werewidelyusedthroughoutEuropeand requireda
5 log 10 reductionin microbial number within 5 minutes.The European suspen-
siontest doesnot differdrastically fromexistingprotocols,apart fromthe
additionof soiling, whichsimulates in use'conditions.In addition, more stringencyis provided by the precise descriptionof the differentstagesof the test, notably,the preparation of the inoculumand the test conditions,including biocide concentration,contact time,waterhardness, temperatureand as already mentionedsoiling. Followingthe publication of the European bactericidal suspensiontest (CEN, 1997a), a European-fundedresearch programmeAndistand' (EU ContractNo.
658 Handbookof hygiene controlin the foodindustry