products (Robertset al., 1996).As withotheragentsof humanfoodpoisoning,
the number of outbreaksof foodpoisoning attributabletoC. perfringensis
under-reported (Labbe¬, 1993).3.2.8 Mycobacteriumbiofilms
The genus Mycobacterium contains approximately 50 species, which are
divided intorapid growers, slowgrowers andthe human leprosy bacillus
(Collins & Grange,1993).Mycobacteriaare weaklyGram-positive, non-motile,
slender,non-spore-forming, rod-shaped, aerobic and free-living in soil and
water(Payeur, 2000).Theydo not produce appreciableamounts of toxin
substances and do not cause food poisoning (Collins & Grange, 2003).
Mycobacteria are widelydistributedin nature and havebeenisolated from
natural and piped waters, wet soil, mud, compost, grasses, vegetables,
unpasteurisedmilkand butter. Theyhavealsobeenisolated fromdomestic
waterpipesfromwhich theyreadily enterdrinkingwater(Collins & Grange,
2003).M. tuberculosis,M. africanum, M. bovis,M. bovisBCGandM. microti
are collectively referred to as the M. tuberculosis complexbecause these
organismscausetuberculosis (Payeur, 2000).Infectionsin humansand animals
maybe causedby most of the slowlygrowing mycobacteria suchasM. avium,
M. intracellulare,M. scofulaceum,M. kansasii,M. marinum,M. simiae, M.
ulceransandM. xenopi. The onlyrapidlygrowing pathogenic species areM.
chelonaeandM. fortuitum.The principal source of theseinfections seemsto be
water(Payeur, 2000).
A pilotplant pasteuriserwas usedto examine the heat resistance ofM. avium
subsp.paratuberculosis(M. paratuberculosis) duringhightemperatureshort
time(HTST) pasteurisationusing raw milksamplesundervarioustimeand
temperature conditions. Results indicated that low numbers of M.
paratuberculosismayalsosurvive extremeHTSTtreatments(Hammeret al.,
2002).Torvinenet al.(2004)studied16 drinkingwaterdistribution systems in
Finland for growthof mycobacteria by samplingwaterfromwaterworksand in
different parts of the systems. In the experimental part, mycobacterial
colonisationas biofilmson polyvinyl chloridetubes was studied. The isolation
frequencyof mycobacteria increased from35%at the waterworksto 80%in the
systems,and the numberof mycobacteria in the positive samples increased from
15 to 140 cfu/l,respectively.The densities of mycobacteria in the developing
biofilmswerehighestat the distalsitesof the system.Over 90%of the myco-
bacteria isolatedfromwaterdeposits belongedtoM. lentiflavum,M. tusciae,M.
gordonaeand a previously unclassified groupof mycobacteria. Daillouxet al.
(2003)investigatedthe abilityofM. xenopito colonise an experimentaldrinking
waterdistributionsystem.M. xenopiwas foundto be presentin the biofilm
within an hourof introduction.After9 weeks,it was constantly presentin all
outletwatersamples(1±10cfu/100ml) and in biofilmsamples(10^2 ±10^3 cfu/
cm^2 ). Biofilms maybe considered to be the reservoirsfor the survivalofM.
xenopi.Gaoet al.(2002)studied the survivalofM. paratuberculosisin 7 regular
56 Handbookof hygiene controlin the foodindustry