Listeria is a bacterium that is naturally found in soil and water with some individuals acting as carriers. Listeria monocytogenes is a species of Listeria and a food-borne pathogen capable of surviving in the presence and absence of oxygen. Its ability to grow at temperatures as low as 0 °C permits multiplication at typical refrigeration temperatures, greatly increasing its ability to evade control in human foodstuffs. Of the ten species of Listeria, L. monocytogenes has been the only species on record that affects humans; mainly new-borns, pregnant woman and immunocompromised individuals. L. monocytogenes is the bacterium that causes Listeriosis and can be fatal if left untreated or detected.
Food Consulting Services makes use of two types of test for L.monocytogenes; a qualitative and a quantitative test.
Quantitative and qualitative methodology
To detect and confirm Listeria monocytogenes
Listeria monocytogenes detection
This method involves a presence or absence (detection) analysis for a particular micro-organism in 25g of test sample. It involves a two-step enrichment process; the sample is initially weighed and incubated overnight in an enrichment broth followed by the second enrichment step after 24 hours. During this process the bacteria, if present, are able to multiply and increase the sensitivity for L. monocytogenes detection. Qualitative analysis is therefore more sensitive in detecting lower counts of the desired microorganism.
Listeria monocytogenes enumeration
Involves the direct enumeration of microorganisms, by determining the number of colony forming units present in 25g of sample. No enrichment step is involved. Enumeration allows for the analysis of L. monocytogenes at levels higher than 10 cfu/g.
At Food Consulting Services, VIDAS® , a multi-parametric immunoassay system, based on the Enzyme Linked Fluorescent Assay (ELFA) technology, is used for the detection of L. monocytogenes in 25g of sample. It works on the principle of an antibody-antigen reaction.
Importance of testing for Listeria monocytogenes
L.monocytogenes is capable of surviving long periods under various stresses and has the ability to form biofilms, this combined with its natural occurrence in the environment makes it difficult to eliminate once contamination occurs. The food industry is ever evolving and growing to accommodate the needs of the growing world population, due to this increased demand for food products, factories are required to keep up with mass production. Within these food factories five common places (drains, equipment, floors, freezer/ cooling systems and the air system) have given rise to L. monocytogenes survival and replication.
Food Consulting Services is a SANAS Accredited Microbiological Laboratory to ISO/ IEC 17025 and offers additional services such as hygiene audit surveys for kitchens, retail and manufacturing.
To find out how we can help you with accurate microbiological test results, reduce your QC costs, improve your service and reduce your report turn around times, please contact us. We look forward to being your microbiology partners.