conveyprotection to the underlyingmaterials, are findinguse in a number of
applications.Surfaces impregnatedwithbiocides are usedin factories and in the
domestic market, but therehas beensomenegative reaction to the increased use
of biocides in termsof a perceived risk of inducing bacterialresistance, and a
possible perceptionof a reduced needto maintain hygienestandardsin the home
(Gilbertand McBain,2003).Photoactivatedglassand other ceramics,impreg-
nated withtitaniumdioxideto produce a self-cleaning'and antimicrobialeffect are likewise stronglyadvocated by someusers.The unwettableLotuseffect'
treated surface, fromwhichliquids roll, thus removingany residual material or
microorganisms,clearlyrequires some verticalplacement, or a regulardirected
washingeffectto enable `rolling'.Suchtreatmentsmustbe consistentlyapplied
across a surface, and theirresponseto usageovertimealso requires evaluation.
If intended for use as a hygienic surface, then testing methodsappropriatefor
these novelsurfaces and mechanisms of activity mayneedto be developed
(Gibsonet al., 1999).If an inhibitoryeffectneedsto be demonstratedon contact
between cellsand substratum,or if irradiationis required to inactivecells(and
remove soil),or diffusionof a material fromthe surface, presenceof liquidover
the surface, or activation via a wiping process/novelsanitizing agent, thencon-
siderationneedsto be paidto the bestin vitromethodappropriate for demon-
strating the intendedin situeffect, thus strengtheningthe relevance of any in-use
claims that might be madeby manufacturers, and ensuringadequate in-use
performancefor users.So far, general criteria and harmonizedtest methodsto
evaluatethe performanceof antimicrobial coatings,as well as criteria for
specific applications,are lacking(Hartog,2004).A number of test protocols
havebeendescribedwhichare basedon the Japanese Industrial Standard JIS Z
2801:2000.Here,a bacterialcell suspensionis heldin intimate contactwitha
coated surfaceusinga sterile cover(e.g.glass microscopecoverslip)in humid
conditions.Aftera set contact time, the size of the residual bacterialpopulation
is comparedwithan appropriatecontrolcoatingusing standard microbiological
enumerationtechniques.ASTM2180-01couldalsobe modified to examine
coated surfaces (Askew,2004).
34.4 Organic soil
Whena substratum has beenused,or exposedto an environment, its surface
chemistrywill immediatelyalter. Surface-active materials suchas stainlesssteel
will be conditionedwithan organiccoating, whichconveyhydrophobicproper-
ties to a surfacewhichmighthavebeenconsideredhydrophilic(Boulange-
Petermann,1996;Verranet al., 2001c).
Once a surfacehas beenused,fouled and cleaned,the characteristics of the
pristinesurface are irrevocablyaltered (Mettler and Carpentier, 1998).Thusa
new'surfaceusedin hygienictesting procedures wouldbe encounteredonly oncein use: considerationshouldtherefore be paidto the inclusion of aused'
hygienic surfacein suchtesting.
564 Handbookof hygiene controlin the foodindustry