Listeria
monocytogenes is
the causative agent of listeriosis, a disease with a high associated mortality
rate of approximately 20%. Foodborne transmission is recognised as the main
vector for human infection, and as such control of the organism in food chains,
particularly food production environments, is key to ensuring the production of
safe, L. monocytogenes-free food
products. An important aspect of L.
monocytogenes contamination patterns is the occurrence of strains capable
of persisting in food processing environments. These strains are repeatedly
isolated from their local environment, often over periods of many years. Such
strains present an increased risk of cross-contamination from the environment
to the associated food products, and thus represent a greater risk of exposure
to consumers. The underlying reason for such persistence remains unknown;
however recent studies suggest a complex, multi-factor mechanism, the nature of
which may vary from case to case. Comparative genomics of persistent and
non-persistent strains has been utilised to increase the understanding of the
genetic basis for persistence. Increased resistance to disinfectants has been
identified among persistent isolates from different food processing
environments, with genetic markers such as transposons identified as the
underlying mechanism. Biofilm formation, and the interactions of L. monocytogenes with other members of
the local microbiome also appears to influence the colonisation of L. monocytogenes, with Enterococcus gallinarum promoting L. monocytogenes biofilm formation, in
contrast to Janthinobacterium lividum,
which inhibits L. monocytogenes
attachment and biofilm formation. Although persistence appears to be the result
of a complex combination of factors, our increasing understanding in different
aspects is allowing a greater appreciation for the persistence phenotype, and
facilitating design of novel bio-control strategies aimed at controlling, or
eliminating, L. monocytogenes from
food processing environments.