be addedto the wettingsolution. Thesehelpto prevent organisms,removed
fromthe surface(wheretheymaybe moreresistant), beingkilledby residual
sanitiserand therebygiving an artificially' reducedcount. Ideallyswabsshould be processed as soonas possible, althoughthis is often impractical,especially whenoutside laboratories are used.Undersuchcondi- tions,samples shouldbe transported non-frozenat a low temperature<5 ÎC, this can resultin minimaldifferences compared withreal timeanalysis (CCFRA, 2003).Timesof samplingand processing need to be recorded, as wellas deliverytemperature,so that any unusual resultsor significant differences from the norm can be identified and considered when interpreting the results. Variables of timeand wetting agentalso needto be considered and optimised in samplingfor specificpathogens.Appropriate pre-enrichmentmedia should be used,althoughovergrowthby morerapidly growing non-pathogensneedsto be considered. Somemanufacturers may add a surfactant to theirwettingsolutions to improvepick-up'fromthe test surface. Thesecan,in some cases, artificially
increase the numberof colonies counted by breakingup clumpsof organisms
and therebyincreasing the numberof `colony-formingunits'.Concernsoverthe
inability of swabbudsto release recovered organisms haveprompted one
manufacturerto develop a radically newtypeof swab.Thislacksthe normal
fibrousbud,whichis replaced withshorttexturedflockednylonin spatula or
swabformat. This devicereleases more of the organismsremoved froma
surfaceand can yieldan approximate1 log improved overallrecoverycompared
withtraditionalswabs(Griffith and Moore, 2004).An alternative approachhas
led to a developmentof a wet or dry vacuumbacterial collection system. This
may be of particular use in pathogentesting as it allows a much larger surfaceto
be testedwithout the need/use of a swabto lift/removethe organism fromthe
surfacebeing tested.
Otherrecentvariationsin swabbing includethe use of petrifilmsto replace
traditionalagarplatesfor cultivation. These are small,thin filmscoated with
nutrients and gelling agents. Afterwetting the film withapproximately 1 ml of
de-ionised waterto rehydrate the growth medium,it can be usedto providea
surfacecount.Anothervariation involvesself-containedmedia and hygiene
swabsin tubeswiththe potentialto offermorerapidresults (Moore and Griffith,
2002b). A traditionalswab,aftertesting a surface,is returned to its accom-
panyingculture tubecontaining semi-solidagarincorporating an indicator.
Microorganisms removedfromthe surface and retained by the swabgrowand,
as they multiplyin the semi-solidagar, the indicatorchanges colour.The results
are semi-quantitative in that the number of bacteriais not recordedbut the time
takenfor the indicatorto changecolour is a measure of the originalmicrobial
load.Uncleansurfaces, depending uponthe extentof microbial contamination,
can test positivewithin12 hours.
Spongesworkon a similar principleto swabbing, in that microorganismsare
removed, released and cultivated.Recoveryis by wipinga compressedsterile
sponge(e.g.cellulose acetate) of varyingsizesoverthe test surface. Mosthave
Improvingsurfacesamplingand detection of contamination 601