the biofilm formedaffectsthe wayin whichthe surfacesshouldbe cleaned.
Oulahal-Lagsiret al. (2003) showed in theirstudies that proteolytic and
glycolyticenzymetreatmenttogether withultrasonics enhance the removalofE.
colibiofilmfromstainlesssteelsoiledwithmilk.These findings correspond
withresultsobtainedin the foodindustry.
3.2.3 Campylobacterbiofilms
Campylobacterspp.are microaerophilic, verysmall, curved and thinGram-
negative rods(Price& Tom,2003a). Growth can occurin a microaerophilic
atmospherecontaining 3±15%oxygenand 3±5%carbon dioxideat 30±48ÎC
witha maximalgrowth rate at 42±43ÎC. The minimumawfor growth is above
0.987. The optimum pH for growthis approximately 6.5±7.5,witha minimumat
4.9 and a maximum at 9.0 (Stern & Kazami,1989;Robertset al., 1996;van
Vliet & Ketley,2001).C. coliandC. laridiscan growat 30.5 ÎC whileC. jejuni
cannot.C. laridistolerates slightly moresalt thanC. jejuniorC. coliand ceases
growing in the presenceof 2.5%sodiumchloride (Robertset al., 1996).Illness
can be causedby ingestionof as few as 500±800cellsin milk.Sincethe
infectivedoseis ratherlow and the foodin manycases maycontainonlya few
cells, liquid enrichment methods are normally required before plating on
selectivemediain orderto detectcontaminationwithC. jejunior C. coli.
Successfuldetectionof theseorganismsrequires incubation at 42 ÎC under
microaerophilicconditions(Robertset al., 1996).
In laboratorytestsCampylobacterhas been shownto forma biofilmin
optimum circumstances on stainlesssteeland glassbeadsin 2 days(Somerset
al., 1994;Dykeset al., 2003).In studiesperformedby de Beeret al.(1994)
biofilms are shown to form zones with low oxygen content in aerobic
surroundingsand Campylobacterspp. can therefore moreeasily survive in
biofilms.Trachooet al.(2002)showedthat viableC. jejunicellsgrownon
polyvinylchloride surfaces decreased withtime and the greatest reduction
occurred on surfaces without a pre-existing biofilm.The number of viableC.
jejunideterminedby using a directviablecountwasgreaterthanby using
culturing techniques, whichindicatesthatC. jejunicellscan forma viablebut
non-culturable statewithinthe biofilm.Bothdeterminationmethodsshowedthat
biofilmsenhance the survivalofC. jejuniduringa 7-dayperiodat 12 ÎC and
23 ÎC (Trachooet al., 2002). Taking the resistance of the viable but non-
culturableC. jejunicells into account is importantin the optimisationof
cleaningand decontamination procedures, especiallyin thosefoodindustrial
processes in whichraw meatproductsare processed (Roweet al., 1998;Trachoo
& Frank,2002).Organic soil,e.g. foodresidues, or moisture improve the
survival of campylobacteron surfaces(Humphreyet al., 1995;Kusamaningrum
et al., 2003).Boucherand co-workers(1998)showedthatC. jejunisurvived
verywellon wooden surfacesbecause the poresin the woodprotectthe cells
fromoxygen.
52 Handbookof hygiene controlin the foodindustry