Listeria Monocytogenes

Topics: Listeria monocytogenes, Listeriosis, Bacteria Pages: 9 (2706 words) Published: June 15, 2008
Listeria monocytogenes is a gram-positive motile facultative anaerobe that inhabits a variety of environments. Using selective media it can be readily isolated from soil, water, vegetation and processed products, including ready-to-eat products designated for human consumption (Graves et al., 1992). The bacterium was named monocytogenes because one distinguish characteristic of infection in rabbits, which was the production of monocytosis in blood (Shuin et al., 1982). L. monocytogenes is phychrophilic, has a temperature for growth of 0°C to 45°C (Barbosa et al., 1994), and enjoys a competitive advantage against other gram-positive and gram-negative microorganisms in cold environments, such as refrigerators. Recent investigations indicate that the organism can initiate growth at pH values as low as 4.4. Also, it grows optimally at water activity of 0.97. For the majority of strains, the minimum water activity needed for growth is 0.93 (Lou et al., 1999); however, some strains may be able to grow at water activity values as low as 0.90 and survive for long periods of time at 0.83 (Shahamat et al., 1980). L. monocytogenes is able to grow in the presence of 10 to 12% sodium chloride; it grows to high populations in moderate salt concentrations (6.5%). The bacterium survival in high-salt environments is significantly increased by lowering the temperature.

Route of Exposure
L. monocytogenes is particularly interesting as a foodborne pathogen in that it is ubiquitous in nature. The current understanding of human listeriosis epidemiology suggests that the organism is a common contaminant of food products. This contamination usually takes place on the surface of the products, with up to 15% harboring the organism. The presence of L. monocytogenes in the food processing chain is evidence by the widespread distribution of the listeriae in processed products. Occurrence of sporadic listeriosis appears to be more common in the spring and summer months. This could be explained by seasonal variations in the type of food products eaten by human populations, with higher-risk products eaten in the warmer months. Some outbreaks investigations suggest that certain ready-to-eat processed foods pose a high risk of contracting listeriosis for susceptible populations. These foods are usually preserved by refrigeration and offer an appropriate environment for the multiplication of L. monocytogenes during manufacture, aging, transportation and storage.

The entry of L. monocytogenes into food processing plants occurs through soil on clothing or equipments, contaminated hides or surfaces, and possibly healthy human carriers. The humidity and presence of nutrients support the growth of Listeria, which is commonly found in moist areas such as processing equipment, drains, etc (Cox et al., 1989). In addition, Listeria can attach to different types of surfaces and biofilm formation has been observed in meat and dairy processing environment (Jeong et al., 1994).

Post-processing contamination is the most likely route of contamination of processed foods. Currently, there is no evidence to indicate that L. monocytogenes can survive heat processing protocols. However, because it is a frequent contaminant of raw material used in food processing plants, there are plenty opportunities for reintroduction of listeriae into food processing facilities by cross contamination (Doyle, 1988). If the product is contaminated during its elaboration, the bacteria can survive and multiply throughout storage causing disease when it is consumed. In conclusion, epidemiologic investigations have repeatedly revealed that the consumption of contaminated food is the primary mode of transmission of listeriosis. Food has been identified as the vehicle of several major outbreaks of listeriosis investigated since 1981.

Food Associated
Some of the food products associated with L. monocytogenes include unpasteurized milk and products prepared from unpasteurized...

References: Barbosa, W.B., Cabedo, L., Wederquist, H.J., Sofos, J.N., Schmidt, G.R. 1994. Growth variations among species and strains of Listeria monocytogenes. J. Food Prot. 57:765-769.
Center of Disease Control and Prevention (CDC). 2005. Listeriosis. Available at: Accessed 21 November 2006.
Charpentier, E., Courvalin, P
Cossart, P. 1995. Actin-based bacterial motility. Curr. Top. Cell Biol. 7:94-101.
Cox, L., Kleiss, T., Cordier, J., Cordellana, C., Konkel, P., Pedrazzini, C., Beumer, R., Siebenga, A. 1989. Listeria spp. in food processing, non-food and domestic environments. Food Microbiol. 6:49-61.
Dalton, C.B., Austin, C.C., Sobel, J., Hayes, P.S., Bibb, W.E., Graves, L.M., Swaminathan, B., Proctor, M.E., Griffin, P.M. 1997. An outbreak of gastroenteritis and fever due to Listeria monocytogenes in milk. N. Engl. J. Med. 336:100-105.
Doyle, M. 1988. Effect of environmental and processing conditions on Listeria monocytogenes. Food Technol. 42:169-171.
Farber, J.M., Peterkin, P.I. 1999. Listeria, Listeriosis and Food Safety: Incidence and behavior of Listeria monocytogenes in meat products. 2nd ed. Marcel Dekker, Inc. New York, United States. 505-564 p.
FDA/Center for Food Safety and Applied Nutrition USDA/Food Safety and Inspection Service October 21, 2003
Goulet, V., Marchetti, P
Hof, H., Nichterlein, T., Kretschmar, M. 1997. Management of listeriosis. Clin. Microbiol. Rev. 10:345-357.
Jeong, D., Frank, J. 1994. Growth of Listeria monocytogenes at 10°C in biofilms with microorganisms isolated from meat and dairy processing environments. J. Food Prot. 57:576-586.
Jinneman, K.C., Wekell, M.M., Eklund, M.W. 1999. Listeria, Listeriosis and Food Safety: Incidence and behavior of Listeria monocytogenes in fish and seafood. 2nd ed. Marcel Dekker, Inc. New York, United States. 601-630 p.
Kessler, S.L., Dajani, A.S. 1990. Listeria meningitis in infants and children. J. Pediatr. Infect. Dis. 9:61-63.
Kolb-Maurer, A., Gentschev, I., Fries, H.W., Fiedler, F., Brocker, E.B., Kampgen, E., Goebel, W. 2000. Listeria monocytogenes-infected human dentritic cells: uptake and host cell response. Infect. Immun. 68:3680-3688.
Kruse, H., Surum, H. 1994. Transfer of multiple drug resistance plasmids between bacteria of diverse origins in natural microenvironments. Appl Environ Microbiol. 60: 4015-4021.
Levy, S.B. 1994. Balancing the drug-resistance equation. Trends Microbiol. 2:341-342.
Lorber, B. 1997. Listeriosis. Clin. Infect. Dis. 24:1-9.
Lou, Y., Yousef, A.E. 1999. Listeria, Listeriosis and Food Safety: Characteristic of Listeria monocytogenes important to food processors. 2nd ed. Marcel Dekker, Inc. New York, United States. 131-224 p.
Pron, B., Boumalia, C., Jaubert, F., Sarnacki, S., Monnet, J.P., Berche, P., Gaillard, J.L. 1998. Comprehensive study of the intestinal stage of listeriosis in a rat ligated loop system. Infect. Immun. 66:747-755.
Rao, G. 1998. Risk factors for the spread of antibiotic-resistant bacteria. Drugs 55:323-330.
Rocourt, J., Jacquet, C., Reilly, A. 2000. Epidemiology of human listeriosis and seafoods. Int. J. Food. Microbiol. 62:197-209.
Shahamat, M., Seaman, A., Woodbine, M. 1980. Survival of Listeria monocytogenes in high salt concentrations. Zentbl. Bakteriol. Hyg. Abt. 1 Orig. A. 246:506-511.
Shuin, D.T., Galsworthy, S.B. 1982. Stimulation of monocyte production by an endogenous mediator induced by a component from Listeria monocytogenes. Immunology. 46:343-351.
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