3.2 Pathogensin biofilms
It is somewhatalarmingto know thatpathogenssuchas Escherichiacoli
O157:H7,Listeriamonocytogenes,SalmonellaTyphimurium,Campylobacter
jejuniandYersinia enterocoliticacan easilyproducebiofilms or be partof
biofilm communities that causeseveredisinfectionand cleaning problemson
surfacesin the foodindustry (Somerset al., 1994;Griffiths,2003;Stopforthet
al., 2003b). Accordingto a studyby Peterset al.(1999)pathogenswereisolated
frombiofilmcommunities.In this studyListeriaspp. werefoundin 35%of food
contact sitesand 42%of environmentalsites,withStaphylococcus aureusbeing
present in a total of 7% and 8%, respectively.Josephet al.(2001)havereported
pathogenicbacteriasuchasKlebsiellaspp.,Campylobacterspp.and entero-
haemorrhagicE. coliin biofilms.
In laboratorystudies, specificproperties of pathogensin biofilms havebeen
studied, and it has beenfoundthat biofilmcells ofListeriaweremoreresistant
than planktonic cells to disinfectants containing, e.g., chlorine, iodine,
quaternaryammonium and anionic acid compounds(Wirtanen,1995;Chae&
Schraft, 2000;Lunde¬n, 2004; Wirtanen& Salo,2004).Chae and Schraft (2000)
used 13 L. monocytogenesstrainsin biofilm studieson glass surfaces at static
conditionsof 37 ÎC for up to 4 days.After3 h incubationbacterialcellsfromall
13 strainshad attached themselves to the glassslidesand theyformedbiofilms
within 24 hours. Twopoultryisolates ofSalmonellawereusedto studybiofilm
formation on three commonlyusedfoodcontact surfaces viz. plastic,concrete
and stainlesssteel.Bothisolates,i.e.SalmonellaWeltevredenandSalmonella
FCM40, showedsimilarpatternsin the biofilmformation withthe greatest
growth on plastic followedby concrete and stainlesssteel (Josephet al., 2001).
In the followingchapters thereare moreexamples of the biofilmformation
capability of someGram-negativeand Gram-positivepathogenicbacteria.
3.2.1 Salmonellabiofilms
Salmonellais a genuswithin the familyEnterobacteriaceaein whichapproxi-
mately 2200serotypesare recognised.Someof thesestrains are specifically
adapted to hosts and largely restrictedto them,e.g.S.Typhi in manandS.
Dublin in cattle.Salmonellais a non-spore-formingrod-shaped, motileGram-
negative bacteriumwith non-motile exceptionssuchasS.GallinarumandS.
Pullorum(Price& Tom,2003b).Salmonellaserotypesare traditionally named
as if theywereseparatespeciesbut, becauseof theirgenetic similarity,a single
species,S. enterica, has beenproposed, withfood-poisoning serotypesmostly
classifiedsubspecies,also namedenterica(Mead,1993).The growthrangefor
salmonellaeis 5±47 ÎC at pH 4.0±9.0,withoptimum growthat 35±37 ÎC and pH
6.5±7.5. Salmonellae are not particularly salt-tolerant,althoughgrowth can
occurin the presenceof 4% sodium chloride. The lowerlimitof wateractivity
(aw) permittinggrowthis 0.93 (Mead, 1993).
Foods commonlyassociated withthe disease includeraw meats,poultry,
eggs,milk and dairyproducts (Price& Tom,2003b). Milk-bornesalmonellosis
50 Handbookof hygiene controlin the foodindustry