relies on cultivation, which,depending on the organism can be hours,daysor
weeks (e.g.for TB).
Mostswabbing protocols are baseduponthe swab-rinsetechnique originally
developedby Manheimerand Yheunezin 1917(Faveroet al., 1968).A sterile
swab, consisting of a moreor less flexibleshaftwitha fibrousbud or tip, is pre-
moistenedin an appropriatewettingagentand inoculatedby rubbingoverthe
surface to be tested. The microorganismstransferredto the swab can thenbe
cultivatedand counted,eitherby inoculating the swabdirectlyontoan appro-
priate solidculturemediumor by releasing intoa known quantity of sterile
recoverydiluent,whichis thenusedto prepare pourplates. Thisdescriptionof
swabbingalsoindicatessome of the variability in the technique,whichcan
considerablyaffect the apparentnumber of organismsrecovered(Moore and
Griffith,2002a).If the number of microorganismson a surfaceis known (as in
laboratoryconditions),and comparedwiththe number obtained fromswabbing,
thereis low recoveryparticularly at low surface populationdensities below 104
cells per cm^2 (Holahet al., 1988).Additionallythe swabbing technique lacks
reliability,i.e. repeatabilityand reproducibility are poor (Moore and Griffith,
2002a,b; Mooreet al., 2001).Various`standard'methodsare recommended,
including by the EU.An ISO Standard (ISO/FDIS 18593) has alsobeen
produced but currentlythereis no universally acceptedmethodof swabbing in
use. Someof the possible variablesare indicated in Fig. 36.5and Table36.4.
Swabbingis widely usedin industryto assess surfacecontaminationand as a
referencefor comparisonwithother methods. However, basicinformation is still
lackingas to the optimum protocol and the effect that variations mayhaveon
recoveryrates(Moore and Griffith,2002a).Overall recovery can be seenas a
function of the removalof microorganismsfromthe test surface, theirrelease
fromthe swaband theirsubsequentability to grow.Recovery rateswill depend
on the techniqueusedbut an optimumrecovery of 10%for Dacronswabs is not
uncommon.Microorganismscan becomeincreasinglydifficult to removefroma
surface once they haveadhered, particularly if associated witha biofilm.
Additionally, organismretention withinthe bud fibres mayalsoleadto poor
repeatability and reduced counts. Techniques/variables that improve one
elementof the swabbingprocess mayadversely affectanother. Onestudy
(Moore and Griffith,2002a)showed protocolsthat improved removal, adversely
affectedrelease.Optimumoverallrecoverymaytherefore be a trade-off or
compromise between different components of the whole process.
The lackof repeatability can make it difficult to interpretthe resultsfrom
environmental swabbing, especiallybetween staff,fromdifferentplants and
when differentprotocolsare used.An apparent low surfacecountfroma single
swab may reflect swabbing techniqueas much as low contamination levels. This
maygivea falseimpressionof cleaningefficacyand if guidelinesor company
specificationshavebeenachieved(see Section 36.5.2). Swabbing,as withother
surface assessment techniques, is bestused to establish trends in the per-
formance of the cleaningand disinfectionprogramme, where overa periodof
time, the programme can be seento be failingor improving. The foodmanu-
598 Handbookof hygiene controlin the foodindustry