SMT4-CT98-2222)has beenundertakento assessthe reproducibilityof the
methodbetween 16 laboratoriesin eight Europeancountries.The workshowed
that the mean precisionof the log reductionfactorin the test was 3 log orders
whena singletest was performed,2 log orders whenfour testswereperformed
and 1 log orderwhenninetests were performed.Thiswork,for the first time,
gavean ideaof the true precisionof suspensiontests.
Surfacetests
Thereare many surfacetests availablefromthe literatureand theycannotall be
described here. Surface testsare particularly appropriatefor the efficacytesting
of disinfectants/sanitisers.Thesetestsattempt to reproducereal-life conditions
wherebythe antimicrobialcompoundis addedontoan inoculumpreviously
driedon a surface. Survivorsare thenrecovered fromthe surfaceand counted,
usuallyaftera neutralisationstep.Protocols can be easilyadaptedto represent
bettersurface conditionsin situ, withthe use of a rangeof porousand non-
poroussurfaces (e.g.varioustextiles, ceramic,stainlesssteel), and specific
microbial environments withthe use of specificmicroorganismsassociatedwith,
for example, the foodor healthcare environments. An alternativeto surfacetests
consists of incorporatingthe biocidal agentinto a surface/product(e.g.textile).
The microbial inoculumis thenaddedonto the surfaceand aftera set contact
time,survivors are counted, usuallyafter a neutralisationstep. In principle,
surfacetestsare easilydesignedbut sufferfroma narrowrangeof applications
and theirreproducibility as compared with suspensiontestsis unknown. The
inoculumdriedon the surfaceis difficult to standardise,notablysince some
microorganismscan be severely injured or killedby the dryingstep(e.g.Ps.
aeruginosa). This severely limits the practicality of thesetestsby decreasing
theirdetection thresholdlimit. Relative humidity thenbecomes an important
factoras wellas the mediumusedto resuspendthe cellsfromthe surface. In
addition, longdryingtimesmay increase the insusceptibility of a microorganism
(vanKlingerenet al., 1998).The reproducibilityof thesetestsbetween labora-
toriesis also questionable(Reybrouck,1986,1990;Bloomfieldet al., 1994).
The developmentof standard carrier test providessomestandardisationfor
surfaceprotocols.The AOACUse-Dilution Testis a well-used carriertest, for
whicha pieceof clothis artificiallycontaminated,driedand immersed in the
disinfectant.It suffered originally fromsome lackof reproducibility, notably
withPs. aeruginosa. Thistest was modified to resultin the AOAC HardSurface
Carrier Test (HSCT) (Beloain, 1993), which was further improved by a
standardisationof the inoculum(Rubinoet al., 1992;Hamiltonet al., 1995;
Beloain, 1995).
In Europe, CEN/TC216 published a bactericidal and fungicidal surface test
(CEN13697,2001)and other practicaltests are beingdeveloped(Holah, 2003).
Suchpracticaltestswill undoubtedlysupersedeexistingcarriertest protocols
published by, for example, DGHM and AFNOR. In the EN 13697a standardised
inoculumis dried on the surface of stainless steel disks, onto which the
appropriatedilutionof the product is added.After a set contact time, the disk is
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