The Full Wiki

More info on Listeria monocytogenes

Listeria monocytogenes: Map


Wikipedia article:

Map showing all locations mentioned on Wikipedia article:

Listeria monocytogenes is a facultative intracellular bacterium that is the causative agent of Listeriosis. It is one of the most virulent foodborne pathogens with 20 to 30 percent of clinical infections resulting in death . Responsible for approximately 2,500 illnesses and 500 deaths in the United States (U.S.) annually, Listeriosis is the leading cause of death among foodborne bacterial pathogens with fatality rates exceeding even Salmonella and Clostridium botulinum.

L. monocytogenes is a Gram-positive bacterium, in the division Firmicutes, named for Joseph Lister. Motile via flagella at 30°C and below but usually not at 37°C,Gründling, A., Burrack, L.S., Bouwer, H.G.A., Higgins, D.E. 2004. Listeria monocytogenes regulates flagellar motility gene expression through MogR, a transcriptional repressor required for virulence. Proc. Natl. Acad. Sci. USA. 101:12316–12323. L. monocytogenes can instead move within eukaryotic cells by explosive polymerization of actin filaments (known as comet tails or actin rockets).

Studies suggest that up to 10% of human gastrointestinal tracts may be colonized by L. monocytogenes.

Nevertheless, clinical diseases due to L. monocytogenes are more frequently recognized by veterinarians, especially as meningo-encephalitis in ruminants. See: listeriosis in animals.

Due to its frequent pathogenicity causing meningitis in newborns (acquired transvaginally), pregnant mothers are often advised not to eat soft cheeses such as Brie, Camembert, feta and queso blanco fresco, which may be contaminated with and permit growth of L. monocytogenes.Genigeorgis, C.,Carniciu, M., Dutulescu, D., Farver, T.B. 1991. Growth and survival of Listeria monocytogenes in market cheeses stored at 4 to 30 degrees C. J. Food Prot. 54(9):662-668. It is the third most common cause of meningitis in newborns.

More recently, L. monocytogenes has been used as the model organism to illustrate the Patho-biotechnology concept.


L. monocytogenes is a gram positive, non-spore forming, motile, facultatively anaerobic, rod shaped bacterium. It is catalase positive, oxidase negative, and expresses a Beta hemolysin which causes destruction of red blood cells. This bacterium exhibits characteristic tumbling motility when viewed with light microscopy. Although L. monocytogenes is actively motile by means of peritrichous flagella at room temperature (20-25C), the organism does not synthesize flagella at body temperatures (37C).

The genus Listeria belongs to the Clostridium sub-branch, together with Staphylococcus, Streptococcus, Lactobacillus and Brochothrix. The genus Listeria includes 6 different species (L. monocytogenes, L. ivanovii, L. innocua, L. welshimeri, L. seegligeri, and L. grayi). Both L. ivanovii and L. monocytogenes are pathogenic in mice, but only L. monocytogenes is consistently associated with human illness. There are 13 serotypes of L. monocytogenes which can cause disease, but more than 90 percent of human isolates belong to only three serotypes: 1/2a, 1/2b, and 4b. L. monocytogenes serotype 4b strains are responsible for 33 to 50 percent of sporadic human cases worldwide and for all major foodborne outbreaks in Europe and North America since the 1980s.


L. monocytogenes was first described by E.G.D.Murray in 1926 based on six cases of sudden death in young rabbits.Murray referred to the organism as Bacterium monocytogenes before J.H. Harvey Pirie changed the genus name to Listeria in 1940. Although clinical descriptions of L. monocyotogenes infection in both animals and humans were published in the 1920s, not until 1952 in East Germanymarker was it recognized as a significant cause of neonatal sepsis and meningitis. Listeriosis in adults would later be associated with patients living with compromised immune systems, such as individuals taking immunosuppressant drugs and corticosteroids for malignancies or organ transplants, and those with HIV infection.

It wasn't until 1981 however that L. monocytogenes was identified as a cause of foodborne illness. An outbreak of listeriosis in Halifaxmarker, Nova Scotiamarkerinvolving 41 cases and 18 deaths, mostly in pregnant women and neonates, was epidemiologically linked to the consumption of coleslaw containing cabbage that had been treated with L. monocytogenes contaminated raw sheep manure. Since then a number of cases of foodborne listeriosis have been reported, and L. monocytogenes is now widely recognized as an important hazard in the food industry.


Infection by L. monocytogenes causes the disease listeriosis. The manifestations of listeriosis include septicemia,Gray, M. L., and A. H. Killinger. 1966. Listeria monocytogenes and listeric infection. Bacteriol. Rev. 30:309-382. meningitis (or meningoencephalitis), encephalitis, corneal ulcer,Holland, S., E. Alfonso, . Gelender, D. Heidemann, A. Mendelsohn, S. Ullman, and D. Miller. 1987. Corneal ulcer due to Listeria monocytogenes. Cornea 6:144-146. pneumonia,Whitelock-Jones, L., J. Carswell, and K. C. Rassmussen. 1989. Listeria pneumonia. A case report. South African Medical Journal 75:188-189. and intrauterine or cervical infections in pregnant women, which may result in spontaneous abortion (2nd/3rd trimester) or stillbirth. Surviving neonates of Fetomaternal Listeriosis may suffer granulomatosis infantiseptica - pyogenic granulomas distributed over the whole body, and may suffer from physical retardation. Influenza-like symptoms, including persistent fever, usually precede the onset of the aforementioned disorders. Gastrointestinal symptoms such as nausea, vomiting, and diarrhea may precede more serious forms of listeriosis or may be the only symptoms expressed. Gastrointestinal symptoms were epidemiologically associated with use of antacids or cimetidine. The onset time to serious forms of listeriosis is unknown but may range from a few days to three weeks. The onset time to gastrointestinal symptoms is unknown but probably exceeds 12 hours. An early study suggeseted that L. monocytogenes was unique among Gram-positive bacteria in that it possessed lipopolysaccharide,Wexler, H., and J. D. Oppenheim. 1979. Isolation, characterization, and biological properties of an endotoxin-like material from the gram-positive organism Listeria monocytogenes. Infect. Immun. 23:845-857. which served as an endotoxin. A later study did not support these findings. SHYAMAL K. MAITRA, RONALD NACHUM, AND FREDERICK C. PEARSON. 1986. Establishment of Beta-Hydroxy Fatty Acids as Chemical Marker Molecules for Bacterial Endotoxin by Gas Chromatography-MassSpectrometry. APPLIED AND ENVIRONMENTAL MICROBIOLOGY, September 1986, p. 510-514

The infective dose of L. monocytogenes varies with the strain and with the susceptibility of the victim. From cases contracted through raw or supposedly pasteurized milk, one may safely assume that in susceptible persons, fewer than 1,000 total organisms may cause disease. L. monocytogenes may invade the gastrointestinal epithelium. Once the bacterium enters the host's monocytes, macrophages, or polymorphonuclear leukocytes, it becomes blood-borne (septicemic) and can grow. Its presence intracellularly in phagocytic cells also permits access to the brain and probably transplacental migration to the fetus in pregnant women. The pathogenesis of L. monocytogenes centers on its ability to survive and multiply in phagocytic host cells.

Regulation of pathogenesis

L. monocytogenes can act as a saprophyte or a pathogen depending on its environment. When this bacteria is present within a host organism quorum sensing causes the up regulation of several virulence genes. Depending on the location of the bacteria within the host organism different activators up regulate the virulence genes. SigB, an alternative sigma factor, up regulates Vir genes in the intestines whereas PrfA up regulates gene expression when the bacteria is present in blood. Little is known about the mechanism in how this bacteria switches between acting as a saprophyte and a pathogen however, it is thought that several non-coding RNAs are required to inducing this change.

Pathogenicity of Lineages

L. monocytogenes has three distinct lineages with differing evolutionary histories and pathogenic potentials . Lineage I strains contain the majority of human clinical isolates and all human epidemic clones, but are underrepresented in animal clinical isolates . Lineage II strains are overrepresented in animal cases and underrepresented in human clinical cases as well as more prevalent in environmental and food samples . Lineage III isolates are very rare but significantly more common in animal isolates than human .


When listeric meningitis occurs, the overall mortality may reach 70%; from septicemia 50%, from perinatal/neonatal infections greater than 80%. In infections during pregnancy, the mother usually survives. Reports of successful treatment with parenteral penicillin or ampicillin exist. Trimethoprim-sulfamethoxazole has been shown effective in patients allergic to penicillin.

Bacteriophage treatments have been developed by several companies. EBI Food Safety and Intralytix both have products suitable for treatment of the bacteria. The Food and Drug Administration of the United States approved a cocktail of six bacteriophages from Intralytix, and a one type phage product from EBI Food Safety designed to kill the bacteria L. monocytogenes. Uses would potentially include spraying it on fruits and ready-to-eat meat such as sliced ham and turkey.

Use as a transfection vector

Because L. monocytogenes is an intracellular parasite, some studies have used this bacteria as a vector to deliver genes in vitro. Current transfection efficiency remains poor. One example of the successful use of L. monocytogenes in in vitro transfer technologies is in the delivery of gene therapies for cystic fibrosis cases.

Cancer vaccine

A live attenuated L. monocytogenes cancer vaccine named ADXS11-001 is under development as a possible treatment for cervical carcinoma.


The methods for analysis of food are complex and time-consuming. The present U.S. Food and Drug Administration (FDA) method, revised in September, 1990, requires 24 and 48 hours of enrichment, followed by a variety of other tests. Total time to identification takes from 5 to 7 days, but the announcement of specific nonradiolabled DNA probes should soon allow a simpler and faster confirmation of suspect isolates.

Recombinant DNA technology may even permit 2-to-3 day positive analysis in the future. Currently, the FDA is collaborating in adapting its methodology to quantitate very low numbers of the organisms in foods.

Bio-Rad Laboratories have come up with media called Rapid'L.Mono Medium which cut short time to 48 hours


Researchers have found L. monocytogenes in at least 37 mammalian species, both domesticated and feral, as well as in at least 17 species of birds and possibly in some species of fish and shellfish. Laboratories can isolate L. monocytogenes from soil, silage, and other environmental sources. L. monocytogenes is quite hardy and resists the deleterious effects of freezing, drying, and heat remarkably well for a bacterium that does not form spores. Most L. monocytogenes are pathogenic to some degree.

Routes of infection

L. monocytogenes has been associated with such foods as raw milk, pasteurized fluid milk,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. 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.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.

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. Note that 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. Three main virulence factors which allow the bacterium to escape are listeriolysin O (LLO - encoded by hly) phospholipase A (encoded by plcA) and phospholipase 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, theL. monocytogenes exploits host actin for the second time. ActA proteins associated with the old bacterial cell pole (being a bacillus, L. monocytogenes septates in the middle of the cell and thus has one new pole and one old pole) are capable of binding the Arp2/3 complex and thus induce actin nucleation at a specific area of the bacterial cell surface. 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.


External links

Embed code:

Got something to say? Make a comment.
Your name
Your email address