38.3 Criteria for testingbiocidal action
The purpose of antimicrobialefficacytestingis to determine a pass/fail criterion
for a given biocide underspecificconditions.At first glance, suchtestsappear
straightforward. However, in reality, to obtainappropriateand reproducible
results,the design of testingprotocols is complex, notably in the numberof
factors that needto be controlled.
38.3.1 Assessmentof antimicrobial activity
Several factorsinfluence the susceptibilityof microorganismsto biocides and
the strictcontrol of these factors is essentialfor the standardisation of testing
protocols. Past studieshavebeenparticularlyprolific in showingthe variations
in growthconditionto the sensitivityprofileof vegetativemicroorganisms and
spores.The results of many laboratory investigations,notably relatingto testing
conditions and microbialgrowthconditions, havehelped in the standardisation
of modern testingprotocols. However, the choice of an appropriateprotocolto
meet all needs is confusing, mostly because of the multitude of methods
available. Indeedseveralstandards havebeenpublishedby differentnational
organisations:in the USA,the AmericanAssociationof Official Analytical
Chemists (e.g.AOAC, 1990);in Germany, the German Society for Hygiene and
Microbiology(DGHM)and the GermanVeterinarySociety(DVG,1988);in
France the French Association of Normalization (AFNOR; e.g. AFNOR, 1989);
and in the UK,the BritishStandardsInstitution (BSI;e.g. Anon 1988).In
Europe, some harmonisationis takingplaceunderthe auspicesof the European
Committee for Standardisation (CEN)by the TechnicalCommittee (TC) 216
(Holah, 2003).
38.3.2 Criteria inherentto the microorganisms
Teststrain
Disinfectantsand sanitisersare expected to havea broadspectrumof activityat
in-use concentration, although some microorganisms are less susceptible,
notablybacterialsporesand to someextent mycobacteria (Table38.5).The
selection of test strains is crucial but often cause for debate. Ideally
antimicrobial testing protocols should use microorganisms that reflect
conditions in situ. However, most standard test protocols recommend the
evaluation of antimicrobial activity against a few selected microorganisms
mainlyfor costand practical reasons.For example,the CEN1276 (1997a)
recommendsthe use ofPseudomonas aeruginosa(ATCC15422),Escherichia
coliATCC(10536),Staphylococcusaureus (ATCC6538) andEnterococcus
hirae(ATCC10541),and for specificapplicationsthe additional bacterialstrains
Salmonella entericaserovartyphimurium(ATCC13311),Lactobacillus brevis
(DSM6235) andEnterobactercloacae(DSM6234). All microorganismsshould
be wellcharacterised and readilyavailablefromculture collections.Teststrains
do not includemicroorganismsthat are knownto be more resistantto a given
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