Control of Listeria monocytogenes on
Food-Contact and Noncontact Surfaces by
Tackling the critical but
persistent problem of biofilm
The number of product recalls attributed to suspected Listeria monocytogenes contamina- tion has increased exponentially since 2013. In 2017, there were at least 100 separate recalls of a diverse range of products, from the traditional soft cheese to the more unusual energy bars.
The reasons for the increased recalls are a combination
of testing with more sensitive diagnostics along with
the power of next-generation sequencing-based typing
techniques.1– 3 Consequently, whereas previously Listeria
in foods would have been missed or attributed to an
unknown source, today, the probability of detection is
From a food safety prospective, product recalls are
an essential step to prevent foodborne illness. On the
counter side, recalls lead to multimillion-dollar losses,
in addition to eroding consumer confidence, or consumers becoming fatigued and inclined not to notice
4 More importantly, recalls represent the failure of industry to control L. monocytogenes
despite the implementation of food safety management
Getting to the Root of Listeria Contamination
In the course of foodborne listeriosis outbreak investigations, a breakdown in plant sanitation is frequently
cited as the root cause.
5 It is well established that L.
monocytogenes can become endemic within processing
environments by building, or becoming incorporated
into, biofilms that can persist for years.
Individual studies have correlated the
persistence of L. monocytogenes with
phenotypic traits such as attachment
strength, biofilm formation, high
growth rate, sanitizer resistance, phage
resistance, expression of stress genes
and low virulence.
7 Yet, an equal body
of evidence has suggested that the
aforementioned phenotypes do not
differ between persistent and transient
L. monocytogenes strains. Moreover, no
genetic differences have been identified
to differentiate persistent versus tran-
8 It has been suggested that
rather than genotypes and phenotypes
of L. monocytogenes, it is the endogenous
population that aids the persistence
of the pathogen by the formation of
biofilms and/or the modulation of the
activity of Listeria.
Sanitation Is Key to
L. monocytogenes Control
The benefits of even the deepest sanitation are lost early into a processing
activity, as both organics and contamination start accumulating on lines along
with the continuation of biofilm formation.
10 Therefore, even a processing
facility operating a diligent sanitation
routine can be open to the risk of establishing an endemic L. monocytogenes
11 It follows that prevention
of biofilm formation is key to controlling Listeria given that once formed, the
films can be difficult, if not impossible,
Antimicrobial Coatings That
Prevent Biofilm Formation
As a supplement to routine sanitation, antimicrobial coatings as a means
of continuous protection against biofilm formation have attracted interest.
Antimicrobial coatings are based on
several principles, the simplest (first
generation) being as a protective coating
By Keith Warriner, Ph.D., and Kayla Murray, M.Sc.