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Challenge Studies to Determine the Ability of Foods to Support the Growth of Listeria monocytogenes
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2018-10-05
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Hunt, K.; Blanc, M.; Álvarez-Ordóñez, A.; Jordan, K. Challenge Studies to Determine the Ability of Foods to Support the Growth of Listeria monocytogenes. Pathogens 2018, 7, 80. https://doi.org/10.3390/pathogens7040080
Abstract
Listeria monocytogenes is a foodborne pathogen that causes listeriosis, a relatively rare, but
potentially fatal, disease, with a mortality rate of 20–30%. In general, European Regulations require
the absence of L. monocytogenes in five samples of 25 g before the food has left the producer, but if
the food has been demonstrated not to support the growth of L. monocytogenes, up to 100 cfu g−1
are allowed in the food (except for foods for infants or medical purposes) during its shelf-life
under reasonably foreseeable storage conditions. It is important for food producers to determine
if their food supports the growth of L. monocytogenes. The European Union Reference Laboratory
for L. monocytogenes published a Technical Guidance document for conducting shelf-life studies on
L. monocytogenes in ready-to-eat foods in June 2014. Primarily based on the EURL guidance document
for conducting challenge studies, the ability of cheese (feta and soft goat’s milk cheese), cold-smoked
salmon, coleslaw, and pork pate to support the growth of L. monocytogenes was determined using a
starting inoculum of approximately 100 cfu g−1
. The cheese and pork pate were incubated at 8 ◦C for
14 days; the smoked salmon was incubated at 6 ◦C for 5 days and 8 ◦C for 9 days; and the coleslaw
was incubated at 8 ◦C for 7 days and 12 ◦C for 14 days. The results showed that the smoked salmon
and pork pate supported growth, while coleslaw and cheese did not. From this study, it is evident
that there are factors in food other than pH, water activity, and total bacterial count (TBC) that can
inhibit the ability of L. monocytogenes to grow in food.