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Listeria monocytogenes is a foodborne human pathogen responsible for invasive infections, overall presenting a high mortality. Despite the ubiquity of the microorganism, the actual disease rate is quite low and the disease is most often associated with an underlying predisposition.
Where is it found?L. monocytogenes is widely distributed in nature. It has been isolated from healthy animals and humans, as well as soils and vegetation.
Listeria monocytogenes is a very persistent bacterium in food processing plants that can survive and grow at very low temperatures. Therefore, L. monocytogenes has become one of the most important microorganisms in the food industry.
Special risk materials are raw or processed meat, raw milk products, raw or smoked �sh, ready prepared salads and long stored vacuum packaged food.
Why is it a problem?L. monocytogenes has been known to cause a serious but rare infection known as listeriosis. Listeriosis is one of the most relevant food-borne diseases.
C/ La Forja, 9 28850 - Torrejón de Ardoz, Madrid - ESPAÑA Tel. +34 91 761 02 00 Fax +34 91 656 82 28
FACTS & IDENTIFICATIONLISTERIA MONOCYTOGENES
Listeria monocytogenes is a pathogenic microorganism that was �rst identi�ed in 1924 by Murray et. al in rabbits. A few years later, in 1929, the �rst human listeriosis outbreaks were observed, but it was not until after many years that this illness was associated with the consumption of contaminated beef and dairy products.
The bacterium is relatively insensitive to high concentrations of salts and acids and is able to multiply at fridge temperature and inside vacuum packaging.
Between 85 and 90% of listeriosis cases result from the ingestion of contaminated products.
Listeriosis is a human disease with low morbidity but high mortality rate (between 20-40%), higher than that caused by Salmonellosis or Campylobacteriosis.
Although some adults experience only mild infections of the eye and skin, and gastroenteritis, it can lead to severe blood poisoning (septicaemia) or meningitis.
Who is especially at risk?Pregnant women, the elderly and people with weakened immune systems, including those su�ering from cancer, AIDS or alcoholism, are more susceptible to listeria.
In pregnant women spontaneous abortion or stillbirth may result.
How can we reduce the risk?Cleaning and disinfection in food processing plants is essential, as well as the use of measures and good practices in handling and the Hazard Analysis and Critical Control Points (HACCP).
To slow the growth of L. monocytogenes, high risk foods should be kept below 4°C and for the shortest time possible.
Avoiding cross contamination of food through good food hygiene and proper food handling can also reduce the risk of infection.
Susceptible individuals can further minimize the risk of listeriosis by taking special dietary precautions, which include avoiding high risk foods.
International regulationsIn the US, any RTE (”ready to eat") food in which the pathogen is detected should be considered adulterated and therefore withdrawn from the market.
In the European Union, RTE foods which are not meant for at-risk-populations as well as those which do not permit the growth of L. monocytogenes, have an imposed limit of 102 cfu/g throughout their shelf-life. Conversely, foods intended for groups at risk, as well as those allowing the growth of the pathogen, are required an absence in 25 g for each analytical unit.
How can we identify it?A variety of culture and rapid methodsbare available for the detection of Listeria spp. in foods. Although the presence of L. innocua may indicate potential contamination with L. monocytogenes, only the latter species is pathogenic for humans. Therefore, the most adequate tests are those which speci�cally detect L. monocytogenes.
There is not a single marker available to test the virulence of �eld isolates for this species. In the future, the combination of di�erent molecular markers will probably allow the screening of food contamination by only the virulent clones of L. monocytogenes, thus improving the prevention of foodborne human listeriosis.
The most commonly used culture reference methods world-wide for the detection of Listeria in foods are the ISO 11290 -1/ISO 11290 -2 standards (ISO, 1996; EC, 1999).
ISO 11290 1/ ISO 11290 - 1 Steps
Listeria monocytogenes is a foodborne human pathogen responsible for invasive infections, overall presenting a high mortality. Despite the ubiquity of the microorganism, the actual disease rate is quite low and the disease is most often associated with an underlying predisposition.
Where is it found?L. monocytogenes is widely distributed in nature. It has been isolated from healthy animals and humans, as well as soils and vegetation.
Listeria monocytogenes is a very persistent bacterium in food processing plants that can survive and grow at very low temperatures. Therefore, L. monocytogenes has become one of the most important microorganisms in the food industry.
Special risk materials are raw or processed meat, raw milk products, raw or smoked �sh, ready prepared salads and long stored vacuum packaged food.
Why is it a problem?L. monocytogenes has been known to cause a serious but rare infection known as listeriosis. Listeriosis is one of the most relevant food-borne diseases.
The bacterium is relatively insensitive to high concentrations of salts and acids and is able to multiply at fridge temperature and inside vacuum packaging.
Between 85 and 90% of listeriosis cases result from the ingestion of contaminated products.
Listeriosis is a human disease with low morbidity but high mortality rate (between 20-40%), higher than that caused by Salmonellosis or Campylobacteriosis.
Although some adults experience only mild infections of the eye and skin, and gastroenteritis, it can lead to severe blood poisoning (septicaemia) or meningitis.
Who is especially at risk?Pregnant women, the elderly and people with weakened immune systems, including those su�ering from cancer, AIDS or alcoholism, are more susceptible to listeria.
In pregnant women spontaneous abortion or stillbirth may result.
How can we reduce the risk?Cleaning and disinfection in food processing plants is essential, as well as the use of measures and good practices in handling and the Hazard Analysis and Critical Control Points (HACCP).
To slow the growth of L. monocytogenes, high risk foods should be kept below 4°C and for the shortest time possible.
Avoiding cross contamination of food through good food hygiene and proper food handling can also reduce the risk of infection.
Susceptible individuals can further minimize the risk of listeriosis by taking special dietary precautions, which include avoiding high risk foods.
C/ La Forja, 9 28850 - Torrejón de Ardoz, Madrid - ESPAÑA Tel. +34 91 761 02 00 Fax +34 91 656 82 28
International regulationsIn the US, any RTE (”ready to eat") food in which the pathogen is detected should be considered adulterated and therefore withdrawn from the market.
In the European Union, RTE foods which are not meant for at-risk-populations as well as those which do not permit the growth of L. monocytogenes, have an imposed limit of 102 cfu/g throughout their shelf-life. Conversely, foods intended for groups at risk, as well as those allowing the growth of the pathogen, are required an absence in 25 g for each analytical unit.
How can we identify it?A variety of culture and rapid methodsbare available for the detection of Listeria spp. in foods. Although the presence of L. innocua may indicate potential contamination with L. monocytogenes, only the latter species is pathogenic for humans. Therefore, the most adequate tests are those which speci�cally detect L. monocytogenes.
There is not a single marker available to test the virulence of �eld isolates for this species. In the future, the combination of di�erent molecular markers will probably allow the screening of food contamination by only the virulent clones of L. monocytogenes, thus improving the prevention of foodborne human listeriosis.
The most commonly used culture reference methods world-wide for the detection of Listeria in foods are the ISO 11290 -1/ISO 11290 -2 standards (ISO, 1996; EC, 1999).
ISO 11290 1/ ISO 11290 - 1 Steps
Listeria monocytogenes is a foodborne human pathogen responsible for invasive infections, overall presenting a high mortality. Despite the ubiquity of the microorganism, the actual disease rate is quite low and the disease is most often associated with an underlying predisposition.
Where is it found?L. monocytogenes is widely distributed in nature. It has been isolated from healthy animals and humans, as well as soils and vegetation.
Listeria monocytogenes is a very persistent bacterium in food processing plants that can survive and grow at very low temperatures. Therefore, L. monocytogenes has become one of the most important microorganisms in the food industry.
Special risk materials are raw or processed meat, raw milk products, raw or smoked �sh, ready prepared salads and long stored vacuum packaged food.
Why is it a problem?L. monocytogenes has been known to cause a serious but rare infection known as listeriosis. Listeriosis is one of the most relevant food-borne diseases.
The bacterium is relatively insensitive to high concentrations of salts and acids and is able to multiply at fridge temperature and inside vacuum packaging.
Between 85 and 90% of listeriosis cases result from the ingestion of contaminated products.
Listeriosis is a human disease with low morbidity but high mortality rate (between 20-40%), higher than that caused by Salmonellosis or Campylobacteriosis.
Although some adults experience only mild infections of the eye and skin, and gastroenteritis, it can lead to severe blood poisoning (septicaemia) or meningitis.
Who is especially at risk?Pregnant women, the elderly and people with weakened immune systems, including those su�ering from cancer, AIDS or alcoholism, are more susceptible to listeria.
In pregnant women spontaneous abortion or stillbirth may result.
How can we reduce the risk?Cleaning and disinfection in food processing plants is essential, as well as the use of measures and good practices in handling and the Hazard Analysis and Critical Control Points (HACCP).
To slow the growth of L. monocytogenes, high risk foods should be kept below 4°C and for the shortest time possible.
Avoiding cross contamination of food through good food hygiene and proper food handling can also reduce the risk of infection.
Susceptible individuals can further minimize the risk of listeriosis by taking special dietary precautions, which include avoiding high risk foods.
International regulationsIn the US, any RTE (”ready to eat") food in which the pathogen is detected should be considered adulterated and therefore withdrawn from the market.
In the European Union, RTE foods which are not meant for at-risk-populations as well as those which do not permit the growth of L. monocytogenes, have an imposed limit of 102 cfu/g throughout their shelf-life. Conversely, foods intended for groups at risk, as well as those allowing the growth of the pathogen, are required an absence in 25 g for each analytical unit.
How can we identify it?A variety of culture and rapid methodsbare available for the detection of Listeria spp. in foods. Although the presence of L. innocua may indicate potential contamination with L. monocytogenes, only the latter species is pathogenic for humans. Therefore, the most adequate tests are those which speci�cally detect L. monocytogenes.
There is not a single marker available to test the virulence of �eld isolates for this species. In the future, the combination of di�erent molecular markers will probably allow the screening of food contamination by only the virulent clones of L. monocytogenes, thus improving the prevention of foodborne human listeriosis.
The most commonly used culture reference methods world-wide for the detection of Listeria in foods are the ISO 11290 -1/ISO 11290 -2 standards (ISO, 1996; EC, 1999).
BIOCHEMICAL PROFILE Listeria spp. Gram- positive, catalase-positive, oxidase- negative, non-spore forming, short rhods, motile at 30ºC or less.
BIBLIOGRAPHY
Food-Borne Pathogenic Microorganisms and Natural Toxins Handbook: “The Bad Bug Book” U.S. FDA/CFSAN. Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park ,2003.
Antle, J.M., 1995. Choice and Efficiency in Food Safety Policy.The AEI Press, Washington, DC.
Elliot T. Riser, Elmer H. Marth “Listeria, Listeriosis and Food Safety”
Kathariou S.”Listeria monocytogenesvirulence and pathogenicity,a food safety perspective.” J Food Prot 2002;65: 1811-29
Rocourt J. “Risk factors for listeriosis.Food Control “.1996; 7: 195-202.
HEMOLYSIS
- +Mannitol Fermentation Rhamnose Fermentation
-
+
+-
Listeria gravi Listeria welshimere
Listeria innocua
Listeria ivanovii londoniensis
Listeria ivanovii
Listeria seeligeri Listeria monocytogens
+ - +- + -
ISO 11290 1/ ISO 11290 - 1 Steps
PREENRICHEMENT
SELECTIVE ENRICHEMENT
SELECTIVE PLATING
CONFIRMATION
LISTERIA HALF FRASER BROTH BASE ( ISO 11290 1) CAT.1183
LISTERIA FRASER BROTH BASE ( ISO 11290 1) CAT.1182
LISTERIA AGAR BASE OXFORD CAT.1133 LISTERIA CHROMOGENIC AGAR BASE ( ISO 11290 1) CAT.1345
GENOTYPE & PHENOTYPE TEST
Xylose Fermentation Xylose Fermentation Xylose Fermentation
C/ La Forja, 9 28850 - Torrejón de Ardoz, Madrid - ESPAÑA Tel. +34 91 761 02 00 Fax +34 91 656 82 28
www.condalab.com . [email protected]
Slutsker L, Schuchat A. Listeriosis in humans. “Listeria, listeriosis and food safety”, 2nd ed. Ryser ET, Marth EH, editors.New York: Marcel Dekker; 1999. p. 75-95
Ottaviani, F., Ottaviani, M. and Agosti, M (1987) Quimper Froid Symposium Proceedings, P6 A.D.R.I.A Quimper (F) 16-18 June ISO 11290-1:2004 Horizontal method for the detection and enumeration of Listeria monocytogenes Part 1: Detection Method.