Listeria monocytogenes: Difference between revisions
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The bacterium is resistant to various environmental conditions, such as high salinity or acidity, which allows it to survive longer under adverse conditions than most other non-sporeforming bacteria of importance in foodborne disease (McCarthy, 1990; Ryser and Marth, 1991). L. monocytogenes occurs widely in food processing environments (Ryser and Marth, 1991, 1999), and can survive for long periods in foods, in processing plants, in households, or in the environment, particularly at refrigeration or frozen storage temperatures. The ability of L. monocytogenes to survive in foods and model systems has been studied extensively, and mathematical models are available that describe the effect of various environmental parameters on the microorganism’s survival (Buchanan and Golden, 1994, 1995, 1998; Buchanan, Golden and Whiting, 1993; Buchanan et al., 1994; Buchanan, Golden and Phillips, 1997). | |||
Although frequently present in raw foods of both plant and animal origin, it is also present in cooked foods due to post-processing contamination if the cooked food is handled post- cooking. L. monocytogenes has been often isolated from food processing environments, particularly those that are cool and wet. L. monocytogenes has been isolated in foods such as raw and pasteurized fluid milk, cheeses (particularly soft-ripened varieties), ice cream, raw vegetables, fermented raw meat and cooked sausages, raw and cooked poultry, raw meats, and raw and smoked seafood (Buchanan et al., 1989; Farber and Peterkin, 1991; FDA/FSIS, 2001; Ryser and Marth, 1991, 1999). Even when L. monocytogenes is initially present at a low level in a contaminated food, its ability to grow during refrigerated storage means that its levels are likely to increase during storage of those foods that can support the growth of the microorganism. A survey of a wide variety of foods from the refrigerators of listeriosis patients in the United States of America found L. monocytogenes in at least one food specimen in 64% of the patient’s refrigerators. Food in 33% of the refrigerators had the same strain as the patient strain (Pinner et al., 1992). However, because the frequency at which people are exposed to L. monocytogenes is much higher than the incidence of listeriosis, there has been a public health debate about the significance of ingesting low levels of the pathogen, particularly for the portion of the population who are not immunologically compromised (Farber, Ross and Harwig, 1996; ICMSF, 1994). | Although frequently present in raw foods of both plant and animal origin, it is also present in cooked foods due to post-processing contamination if the cooked food is handled post- cooking. L. monocytogenes has been often isolated from food processing environments, particularly those that are cool and wet. L. monocytogenes has been isolated in foods such as raw and pasteurized fluid milk, cheeses (particularly soft-ripened varieties), ice cream, raw vegetables, fermented raw meat and cooked sausages, raw and cooked poultry, raw meats, and raw and smoked seafood (Buchanan et al., 1989; Farber and Peterkin, 1991; FDA/FSIS, 2001; Ryser and Marth, 1991, 1999). Even when L. monocytogenes is initially present at a low level in a contaminated food, its ability to grow during refrigerated storage means that its levels are likely to increase during storage of those foods that can support the growth of the microorganism. A survey of a wide variety of foods from the refrigerators of listeriosis patients in the United States of America found L. monocytogenes in at least one food specimen in 64% of the patient’s refrigerators. Food in 33% of the refrigerators had the same strain as the patient strain (Pinner et al., 1992). However, because the frequency at which people are exposed to L. monocytogenes is much higher than the incidence of listeriosis, there has been a public health debate about the significance of ingesting low levels of the pathogen, particularly for the portion of the population who are not immunologically compromised (Farber, Ross and Harwig, 1996; ICMSF, 1994). | ||
Revision as of 18:51, 22 July 2014
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]
Overview
Listeria monocytogenes is a Gram-positive bacterium, in the division Firmicutes, named for Joseph Lister. Motile via flagella, L. monocytogenes can move within eukaryotic cells by explosive polymerization of actin filaments (known as comet tails or actin rockets). The name monocitogenes derives from the strong monocytic activity this organism produces in rabbits, which however does not happen in humans. Despite the name, more that half the patients present with increased levels of neutrophils in CSF.[1] Studies suggest that up to 10% of human gastrointestinal tracts may be colonized by L. monocytogenes.
Taxonomy
Bacteria; Firmicutes; Bacilli; Bacillales; Listeriaceae; Listeria; Listeria monocytogenes
Biology
Listeria monocytogenes is a Gram-positive, facultative anaerobe, nonsporulating bacillus with polar flagellae. It is a catalase-positive organism and exhibits motility, more specifically tumbling motility (between 20-25ºC). At 35 ºC the bacterium looses its motility. Listeria produces acid but not gas in a variety of carbohydrates.[2] It has the ability to grow at temperatures between 0°C and 45ºC, which allow it to survive in a diverse array of environments such as soil, water, food products, and host cells. It can grown in an environment where the pH level ranges from 4.4 and 9.4
Listeria uses the cellular machinery to move inside the host cell. It induces directed polymerization of actin by the ActA transmembrane protein, thus pushing the bacterial cell inside the host cell.
Infectious Cycle
The primary site of infection is the intestinal epithelium where the bacteria invade non-phagocytic cells via the "zipper" mechanism:
- Uptake is stimulated by the binding of listerial internalins (Inl) to host cell adhesion factors such as E-cadherin or Met.
- This binding activates certain Rho-GTPases which subsequently bind and stabilize Wiskott-Aldrich syndrome protein (WASp).
- WASp can then bind the Arp2/3 complex and serve as an actin nucleation point.
- Subsequent actin polymerization extends the cell membrane around the bacterium, eventually engulfing it.
- The net effect of internalin binding is to exploit the junction forming-apparatus of the host into internalizing the bacterium.
L. monocytogenes can also invade phagocytic cells (e.g. macrophages) but only requires internalins for invasion of non-phagocytic cells.
- Following internalisation, the bacterium must escape from the vacuole/phagosome before fusion with a lysosome can occur. Two main virulence factors allow the bacterium to escape:
- Listeriolysin O (LLO - encoded by hly)
- Phospholipase C B (plcB).
- Secretion of LLO and PlcB disrupts the vacuolar membrane and allows the bacterium to escape into the cytoplasm where it may proliferate.
- Once in the cytoplasm, L. monocytogenes exploits host's actin for the second time:
- ActA proteins associated with the old bacterial cell pole, are capable of binding the Arp2/3 complex and thus induce actin nucleation at a specific area of the bacterial cell surface (being a bacilli, L. monocytogenes septates in the middle of the cell and thus has "new pole" and another "old pole").
- Actin polymerization then propels the bacterium unidirectionally into the host cell membrane. The protrusion which is formed, may then be internalised by a neighbouring cell, forming a double-membrane vacuole from which the bacterium must escape using LLO and PlcB.
Tropism
Natural Reservoir
Listeria monocytogenes is broadly distributed throughout the environment. It is commonly found in soil, water, vegetation and fecal material. Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin, such as meats and dairy products.
L. monocytogenes has been associated with such foods as raw milk, pasteurized fluid milk[3], cheeses (particularly soft-ripened varieties), ice cream, raw vegetables, fermented raw-meat sausages, raw and cooked poultry, raw meats (of all types), and raw and smoked fish.
Its ability to grow at temperatures as low as 0°C permits multiplication in refrigerated foods. In refrigeration temperature such as 4°C the amount of ferric iron promotes the growth of L. monocytogenes.[4]
References
- ↑ Mandell, Gerald L.; Bennett, John E. (John Eugene); Dolin, Raphael. (2010). Mandell, Douglas, and Bennett's principles and practice of infectious disease. Philadelphia, PA: Churchill Livingstone/Elsevier. ISBN 0-443-06839-9.
- ↑ Chapter 13. Non-Spore-Forming Gram-Positive Bacilli: Corynebacterium, Propionibacterium, Listeria, Erysipelothrix, Actinomycetes, & Related Pathogens ,Jawetz, Melnick, & Adelberg's Medical Microbiology, 24th Edition ,The McGraw-Hill Companies
- ↑ Fleming, D. W., S. L. Cochi, K. L. MacDonald, J. Brondum, P. S. Hayes, B. D. Plikaytis, M. B. Holmes, A. Audurier, C. V. Broome, and A. L. Reingold. 1985. Pasteurized milk as a vehicle of infection in an outbreak of listeriosis. N. Engl. J. Med. 312:404-407.
- ↑ Dykes, G. A., Dworaczek (Kubo), M. 2002. Influence of interactions between temperature, ferric ammonium citrate and glycine betaine on the growth of Listeria monocytogenes in a defined medium. Lett Appl Microbiol. 35(6):538-42.