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Listeria monocytogenes is one of the main foodborne pathogens which causes nearly 1600
illnesses due to listeriosis resulting in 19% deaths in the United States
annually (Scallan et al., 2011). During 2011, the whole cantaloupe caused an outbreak due to
contamination with Listeria monocytogenes (CDC, 2011; McCollum  et al., 2013).
It was supposed that the bacteria in an inaccessible places formed biofilm and
then started to invade the product (Sapers, 2001). Furthermore, many of dairy products were incriminated in the frequent
incidence of Listeria monocytogenes outbreaks as ice cream (Régis et al., 2016) and soft
cheese (Choi et al., 2014; Crowe et al.,
2015; Heiman et al., 2016) which
can be attributed to the ability of this bacteria to form biofilm on dairy
equipment representing a potential source for milk and dairy products contamination
(Latorre et al., 2010; Waak et al., 2002). Biofilms are broadly
defined as microbially derived sessile form, where the bacterial cells attach either
to a surface or to each other producing extracellular polymeric substance (EPS)
(Donlan and
Costerton, 2002; Giaouris et
al., 2014; Gkana et al.,
2017; Lazazzera,
2005; Trinetta et
al., 2012). This
exopolysaccharide matrix act as a barrier against cells-sanitizers interaction
protecting bacterial cells from sanitizers’ effect (Kocot and
Olszewska, 2017; Trinetta et
al., 2012; Vaid et al.,
2010). Besides its ability
to form biofilm in the food industry with high numbers (Adrião et
al., 2008; Palmer et
al., 2007; Pan et al.,
2006; Takahashi et
al., 2010), Listeria monocytogenes
acquired a significant attention due to its unique ability to grow in high salt,
low temperatures like a refrigerator,
persisting within biofilms and contaminating the final product, where it
remains viable through the whole shelf life (Camargo et
al., 2017). Therefore, it is a serious
challenge for food industry to control biofilms formed by Listeria
monocytogenes on food contact surfaces for hygienic food production. Furthermore,
routine cleaning regimes of the food
plants are required to prevent and control biofilm formation. This regime should be cheap, time-saving nondestructive
techniques (Weiler et
al., 2013). Listeria
monocytogenes biofilm resistance for antimicrobials depends on its growth
phase and food residues presence (Gram et al.,
2007; Pan et al.,
2006). The effective
sanitizers should possess the ability to penetrate the exopolysaccharide (EPS)
which is biofilm matrix to get access to bacterial cells and kill them through
sufficient concentration and time. Also, it has to be effective where organic
matter are present, because sanitizer’s efficacy is reduced by organic matter
presence (Chen et al.,
2015). Peroxyacetic acid (PAA)
is characterized by high reactivity, oxidizing power besides its low molecular
size and high decomposition rate, which facilitate biofilm breakthrough (Ibusquiza et
al., 2011). Also, it is
effective at low temperatures (0 – 25 oC) and decomposed into safe
non-toxic residues on food surfaces (Lee et al.,
2016). The
aim of this study is to evaluate the antimicrobial efficacy of chemical sanitizers
against single and cocktail Listeria monocytogenes biofilms either fresh
or old. Also, Industrial conditions were simulated through application of diluted
apple juice and whole milk to evaluate the efficacy of these sanitizers.

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