3.2.4 Listeria monocytogenesbiofilms
Listeriamonocytogenesis a facultativelyanaerobicGram-positive,non-spore-
formingshortrod that is widely distributedin nature (El-Kest& Marth, 1988;
Griffiths, 2003).It is a non-hostspecificpathogen(El-Kest& Marth,1988;
Lunde¬n, 2004). Listeriosis may occur sporadically or epidemically. The
organismhas beenisolatedfromraw milk,mastitic milkand pasteurised
milk. Foodstuffs associated with listeriosis outbreaks also include cold-
smokedand gravad rainbowtroutproducts, slicedcoldmeat, soft cheese,
butter,ice-creamand coleslaw.Examplesof epidemicsources are: coleslaw
in Canada1981,unpasteurised milk in the USA1983,Mexican-stylesoft
cheesein USA1985,pork productin France 1992,chocolatemilkin the USA
1994,soft cheesein Swizerland 1995,rainbowtroutin Sweden 1997,cornin
Italy 1997, hot dogs in the USA 1998±99 and butter in Finland 1999
(Lyytika»inenet al., 2000;Weinstein& Ortiz,2001).Treatedwastewatercan
also be a sourceofL. monocytogenes. Of the 13 differentL. monocytogenes
serotypesonlythree(1/2a,1/2band 4b) havebeenpredominantly implicated
in humandiseases(Chae& Schraft,2000).It has beenreportedthat healthy
peoplecan be carriersof L. monocytogenes(El-Kest & Marth, 1988).L.
monocytogenesis able to grow in many environments, at a low oxygen
tensions,in highsalt concentrationsand overa widerangeof pH (5±9.5)and
temperatures (3±45ÎC) withan optimumat 30 ÎC (Griffiths,2003; Lunde¬n,
2004).The bacteriumcan survivefor a limitedtime in up to 25%salt at 4 ÎC
(El-Kest& Marth,1988).
Hygienemonitoringin the foodprocessingindustryis importantbecauseL.
monocytogenes, in particular,can colonise and formbiofilms in foodprocessing
environments and on surfaces (Husuet al., 1990;Eklundet al.1995;Autioet
al., 1999;Miettinenet al., 1999,2001;Lyytika»inenet al., 2000;Aarnisaloet al.,
2003;Lunde¬n, 2004;Miettinen& Wirtanen,2005;Wirtanen & Salo,2004).
Listeriasourcesin processing plantsare conveyor belts,cutters,slicers, brining
and packagingmachines, coolersand freezersas wellas floors and drains
(Wirtanen, 2002;Lunde¬n, 2004;Wirtanen & Salo,2004).L. monocytogeneshas
beenfoundto formbiofilms on commonfoodcontactsurfaces suchas plastic,
polypropylene, rubber as wellas stainlesssteel and also on glass(Mafuet al.,
1990;Helkeet al., 1993;Ronner& Wong,1993;Wirtanen,1995; Chae &
Shraft,2000;Boruckiet al., 2003;Lunde¬n, 2004).
3.2.5 Staphylococcusaureusbiofilms
Staphylococcus aureusis a Gram-positive, aerobic, non-spore-forming catalase
postitiverod. It is ubiquitousin the mucousmembrane and skin of most warm-
blooded animals.Nasaland skin carriage are frequent vehicles in the transporta-
tion ofS. aureus.It is an opportunistic pathogencausinginfections via open
wounds, for example (Robertset al., 1996).The growthtemperature for this
bacteriumis 7±48 ÎC, with an optimum around 37 ÎC. Growth has beendemon-
stratedoverthe pH range4±10,withan optimum at 6±7.The lower limitofaw
Biofilmrisks 53