no swabshaft,and in orderto avoid contamination, the spongeneedsto be held
using a sterile glove, usually provided withthe sponge. Spongesmaybe pre-
moistenedor requirethe additionof a wetting agent.After inoculationthe
spongeis returnedto a sterileenvelope/packetand transported to a laboratory.
After the additionof a suitablediluentto the envelope,usually followedby
agitation/stomaching,the released organismscan be counted.Similar errors to
those encounteredin swabbing may occur, and thereis some evidenceto suggest
thatthe spongematrix retainsevenmoreof the recovered organismsthan
swabbing,resulting in loweroverallrecovery(Mooreand Griffith,2002b).
Some sponges offerthe advantageof greatersurface area:beingmuchbigger
thanconventionalswabstheyallowlargersurfaceareasto be tested, and may
therefore be moreusefulin testingsurfaces for pathogens. Greaterpressurecan
also be applied thanwithswabs.Other variations includesponges on sticks, and
in France,the use of gauzeto swab surfaces.Validation data on the effectiveness
of someof thesealternatives are not widely available.
36.2.2 Replicateorganismdirectareacontact (RODAC)± agar sausages,
contact plates, dipslides
All directagar contact methods, or replicateorganism directareacontact
(RODAC),involvepressing sterileagaronto a surfaceto be sampled.A contact
timeof 10 seconds with a force of 25 g/cm^2 , without lateralmovement, is
suggested (ISO/CD14698-12). Microorganisms are directly transferredontothe
agar surfaceand, afterincubationfor an appropriate lengthof time,multiply and
formcolonies,whichare visibleand can be counted.In generalthis approach is
bestsuitedto smooth,flat surfaces. The methodsvaryin howthe agaris
dispersed.Contact platesresemble smallplasticPetridishes witha lid. The agar
is pouredinto them,leavinga convexcontactsurface. Afterremoving the lid the
agaris pressedontothe test surface. The contact platesare thenincubatedand
examined24±48hours later.
Agar immersion,platingand contact (AIPC) slides, morecommonly referred
to a dipslidesor paddles(in the US), were developedfrom`dip spoons' usedin
counting the numbers of organismsin urinesamples.Theycomprisea double-
sided hinged paddle witha neutralor selective agar,attachedto bothsides.The
paddle is containedwithina transparent cylindrical tube or plasticcontainer.The
dipslide is removed,thenpressed ontothe surface to be tested,replaced back
into the tubeand resultingcolonygrowth counted, or compared withpictorial
estimates/diagramsof surfacecounts. Theycan alsobe usedfor countingthe
number of organismsin liquid samples of food,wateror rinsewater.Recently a
flexible hybrid contactplate/dipslide,to test moreirregular-shaped surfaces,has
become available.
Direct agarcontact methodshavea numberof advantagesand disadvantages
comparedwith traditionalswabbing(see Table36.3).Advantages includeease
of use, generally lowercostsand betterrecoveryand repeatability (Niskanenand
Pohja, 1977;Moore and Griffith,2002b;Mooreet al., 2001).Disadvantages
602 Handbookof hygiene controlin the foodindustry