Listeria
Encyclopedia
Listeria is a bacteria
l genus
that contains seven species. Named after the English pioneer of sterile surgery Joseph Lister
, the genus received its current name in 1940. Listeria species are gram-positive
bacilli
. The major human pathogen
in the Listeria genus is L. monocytogenes. It is usually the causative agent of the relatively rare bacterial disease, listeriosis, a serious infection caused by eating food contaminated with the bacteria. The disease affects primarily pregnant women, newborns, adults with weakened immune systems, and the elderly.
Listeriosis is a serious disease for humans; the overt form of the disease has a mortality rate
of about 20 percent. The two main clinical manifestations are sepsis
and meningitis
. Meningitis is often complicated by encephalitis
, a pathology that is unusual for bacterial infections. Listeria ivanovii is a pathogen of mammals, specifically ruminant
s, and has rarely caused listeriosis in humans.
; however, that name was already in use for a slime mold and a protozoa
n. Eventually, the genus Listeria was proposed and accepted. All species within the Listeria genus are Gram-positive, nonsporeforming, catalase-positive rods. The genus Listeria was classified in the family Corynebacteriaceae through the seventh edition of Bergey’s Manual of Systematic Bacteriology. The 16S rRNA cataloging studies of Stackebrandt, et al. demonstrated that L. monocytogenes is a distinct taxon within the Lactobacillus-Bacillus branch of the bacterial phylogeny constructed by Woese. In 2001, the genus was placed in the newly created Family Listeriaceae. The only other genus in the family is Brochothrix.
The genus Listeria currently contains seven species: L. grayi, L. innocua, L. ivanovii, L. monocytogenes, L. murrayi, L. seeligeri, and L. welshimeri. Listeria dinitrificans, previously thought to be part of the Listeria genus, was reclassified into the new genus Jonesia. Under the microscope, Listeria species appear as small, Gram-positive rods, which are sometimes arranged in short chains. In direct smears, they may be coccoid, so they can be mistaken for streptococci. Longer cells may resemble corynebacteria. Flagella are produced at room temperature, but not at 37 °C. Hemolytic activity on blood agar has been used as a marker to distinguish L. monocytogenes among other Listeria species, but it is not an absolutely definitive criterion. Further biochemical characterization may be necessary to distinguish between the different species of Listeria.
Listeria can be found in soil, which can lead to vegetable contamination. Animals are most common carriers. Listeria has been found in uncooked meats, uncooked vegetables, fruit such as cantaloupe
s, unpasteurized milk, foods made from unpasteurized milk, and processed foods. Pasteurization and sufficient cooking kill Listeria; however, contamination may occur after cooking and before packaging. For example, meat-processing plants producing ready-to-eat foods, such as hot dogs and deli meats, must follow extensive sanitation policies and procedures to prevent Listeria contamination. Once an infection occurs in humans, one out of five people die. Once the infection begins in a processing plant, it is almost impossible to eradicate it. Listeria monocytogenes is commonly found in soil, stream water, sewage, plants, and food. Listeria are responsible for listeriosis, a rare but potentially lethal food-borne infection. The case fatality rate for those with a severe form of infection may approach 25%. (Salmonella
, in comparison, has a mortality rate estimated at less than 1%). Although Listeria monocytogenes has low infectivity, it is hardy and can grow in temperatures from 4 °C (39.2 °F) (the temperature of a refrigerator), to 37 °C (98.6 °F), (the body's internal temperature). Listeriosis is a serious illness, and the disease may manifest as meningitis, or affect newborns due to its ability to penetrate the endothelial layer of the placenta
.
by the ActA transmembrane protein
, thus pushing the bacterial cell around.
Listeria monocytogenes, for example, encodes virulence genes that are thermoregulated. The expression of virulence factor is optimal at 37 degrees Celsius and is controlled by a transcriptional activator, PrfA, whose expression is thermoregulated by the PrfA thermoregulator UTR
element. At low temperatures, the PrfA transcript is not translated due to structural elements
near the ribosome binding site. As the bacteria infect the host, the temperature of the host melts the structure and allows translation initiation for the virulent genes.
The majority of Listeria bacteria are targeted by the immune system
before they are able to cause infection
. Those that escape the immune system's initial response, however, spread through intracellular mechanisms and are, therefore, guarded against circulating immune factors (AMI).
To invade, Listeria induces macrophage phagocytic uptake by displaying D-galactose in their teichoic acid
s that are then bound by the macrophage
's polysaccharide
receptors. Other important adhesins are the internalin
s. Once phagocytosed, the bacterium is encapsulated by the host cell's acidic phagolysosome
organelle. Listeria, however, escapes the phagolysosome by lysing the vacuole's entire membrane with secreted hemolysin
, now characterized as the exotoxin listeriolysin O. The bacteria then replicate inside the host cell's cytoplasm.
Listeria must then navigate to the cell's periphery to spread the infection to other cells. Outside the body, listeria has flagellar-driven motility, sometimes described as a "tumbling motility." However, at 37 °C, flagella cease to develop and the bacterium instead usurps the host cell's cytoskeleton
to move. Listeria, inventively, polymerizes an actin
tail or "comet", from actin monomers in the host's cytoplasm with the promotion of virulence factor ActA. The comet forms in a polar manner and aids the bacteria's migration to the host cell's outer membrane. Gelsolin, an actin filament severing protein, localizes at the tail of listeria and accelerates the bacterium's motility. Once at the cell surface, the actin-propelled listeria pushes against the cell's membrane to form protrusions called filopods or "rockets". The protrusions are guided by the cell's leading edge to contact adjacent cells, which then engulf the listeria rocket and the process is repeated, perpetuating the infection. Once phagocytosed, the listeria is never again extracellular: it is an intracytoplasmic parasite like Shigella flexneri
and Rickettsia
.
has published a list of foods that have sometimes caused outbreaks of Listeria: hot dogs, deli meats, raw milk, cheeses (particularly soft-ripened cheeses like feta, Brie, Camembert, blue-veined, or Mexican-style “queso blanco”), raw and cooked poultry, raw meats, ice cream, raw vegetables, raw and smoked fish.
Cantaloupe
has been implicated in an outbreak of listeriosis from a farm in Colorado
, and the Australian company GMI Food Wholesalers were fined AU$236,000 for providing Listeria monocytogenes contaminated chicken wraps to the airline Virgin Blue
.
is an effective topical sanitizer against Listeria. Quaternary ammonium can be used in conjunction with alcohol as a food contact safe sanitizer with increased duration of the sanitizing action. Refrigerated foods in the home should be kept below 4 °C (39.2 °F) to discourage bacterial growth. Preventing listeriosis also can be done by carrying out an effective sanitation of food contact surfaces.
, vancomycin
(unclear effectiveness), ciprofloxacin
, linezolid
, azithromycin
.
Mixtures of bacteriophages have also proven effective in the treatment of Listeria.
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
l genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
that contains seven species. Named after the English pioneer of sterile surgery Joseph Lister
Joseph Lister, 1st Baron Lister
Joseph Lister, 1st Baron Lister OM, FRS, PC , known as Sir Joseph Lister, Bt., between 1883 and 1897, was a British surgeon and a pioneer of antiseptic surgery, who promoted the idea of sterile surgery while working at the Glasgow Royal Infirmary...
, the genus received its current name in 1940. Listeria species are gram-positive
Gram-positive
Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink...
bacilli
Bacilli
Bacilli refers to a taxonomic class of bacteria. It includes two orders, Bacillales and Lactobacillales, which contain several well-known pathogens like Bacillus anthracis .-Ambiguity:...
. The major human pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
in the Listeria genus is L. monocytogenes. It is usually the causative agent of the relatively rare bacterial disease, listeriosis, a serious infection caused by eating food contaminated with the bacteria. The disease affects primarily pregnant women, newborns, adults with weakened immune systems, and the elderly.
Listeriosis is a serious disease for humans; the overt form of the disease has a mortality rate
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...
of about 20 percent. The two main clinical manifestations are sepsis
Sepsis
Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...
and meningitis
Meningitis
Meningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...
. Meningitis is often complicated by encephalitis
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
, a pathology that is unusual for bacterial infections. Listeria ivanovii is a pathogen of mammals, specifically ruminant
Ruminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
s, and has rarely caused listeriosis in humans.
Background
The first documented case of Listeria was in 1924. In the late 1920s, two researchers independently identified Listeria monocyctogenes from animal outbreaks. They proposed the genus Listerella in honor of surgeon and early antiseptic advocate Joseph ListerJoseph Lister
Joseph Lister may refer to:*Joseph Lister, 1st Baron Lister , English surgeon, discovered that cleaning and disinfecting surgical wounds, and bandages, with carbolic acid prevents lethal infections...
; however, that name was already in use for a slime mold and a protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
n. Eventually, the genus Listeria was proposed and accepted. All species within the Listeria genus are Gram-positive, nonsporeforming, catalase-positive rods. The genus Listeria was classified in the family Corynebacteriaceae through the seventh edition of Bergey’s Manual of Systematic Bacteriology. The 16S rRNA cataloging studies of Stackebrandt, et al. demonstrated that L. monocytogenes is a distinct taxon within the Lactobacillus-Bacillus branch of the bacterial phylogeny constructed by Woese. In 2001, the genus was placed in the newly created Family Listeriaceae. The only other genus in the family is Brochothrix.
The genus Listeria currently contains seven species: L. grayi, L. innocua, L. ivanovii, L. monocytogenes, L. murrayi, L. seeligeri, and L. welshimeri. Listeria dinitrificans, previously thought to be part of the Listeria genus, was reclassified into the new genus Jonesia. Under the microscope, Listeria species appear as small, Gram-positive rods, which are sometimes arranged in short chains. In direct smears, they may be coccoid, so they can be mistaken for streptococci. Longer cells may resemble corynebacteria. Flagella are produced at room temperature, but not at 37 °C. Hemolytic activity on blood agar has been used as a marker to distinguish L. monocytogenes among other Listeria species, but it is not an absolutely definitive criterion. Further biochemical characterization may be necessary to distinguish between the different species of Listeria.
Listeria can be found in soil, which can lead to vegetable contamination. Animals are most common carriers. Listeria has been found in uncooked meats, uncooked vegetables, fruit such as cantaloupe
Cantaloupe
"Rockmelon" redirects here, for the band see Rockmelons. See also Cantaloupe .Cantaloupe refers to a variety of Cucumis melo, a species in the family Cucurbitaceae which includes nearly all melons and squashes. Cantaloupes range in size from...
s, unpasteurized milk, foods made from unpasteurized milk, and processed foods. Pasteurization and sufficient cooking kill Listeria; however, contamination may occur after cooking and before packaging. For example, meat-processing plants producing ready-to-eat foods, such as hot dogs and deli meats, must follow extensive sanitation policies and procedures to prevent Listeria contamination. Once an infection occurs in humans, one out of five people die. Once the infection begins in a processing plant, it is almost impossible to eradicate it. Listeria monocytogenes is commonly found in soil, stream water, sewage, plants, and food. Listeria are responsible for listeriosis, a rare but potentially lethal food-borne infection. The case fatality rate for those with a severe form of infection may approach 25%. (Salmonella
Salmonella
Salmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...
, in comparison, has a mortality rate estimated at less than 1%). Although Listeria monocytogenes has low infectivity, it is hardy and can grow in temperatures from 4 °C (39.2 °F) (the temperature of a refrigerator), to 37 °C (98.6 °F), (the body's internal temperature). Listeriosis is a serious illness, and the disease may manifest as meningitis, or affect newborns due to its ability to penetrate the endothelial layer of the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
.
Pathogenesis
Listeria uses the cellular machinery to move around inside the host cell: It induces directed polymerization of actinActin
Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
by the ActA transmembrane protein
Transmembrane protein
A transmembrane protein is a protein that goes from one side of a membrane through to the other side of the membrane. Many TPs function as gateways or "loading docks" to deny or permit the transport of specific substances across the biological membrane, to get into the cell, or out of the cell as...
, thus pushing the bacterial cell around.
Listeria monocytogenes, for example, encodes virulence genes that are thermoregulated. The expression of virulence factor is optimal at 37 degrees Celsius and is controlled by a transcriptional activator, PrfA, whose expression is thermoregulated by the PrfA thermoregulator UTR
PrfA thermoregulator UTR
The PrfA thermoregulator UTR is an RNA thermometer found in the 5' UTR of the prfA gene. In Listeria monocytogenes, virulence genes are maximally expressed at 37°C but are almost silent at 30°C. The genes are controlled by PrfA, a transcriptional activator whose expression is thermoregulated...
element. At low temperatures, the PrfA transcript is not translated due to structural elements
Cis-regulatory element
A cis-regulatory element or cis-element is a region of DNA or RNA that regulates the expression of genes located on that same molecule of DNA . This term is constructed from the Latin word cis, which means "on the same side as". These cis-regulatory elements are often binding sites for one or...
near the ribosome binding site. As the bacteria infect the host, the temperature of the host melts the structure and allows translation initiation for the virulent genes.
The majority of Listeria bacteria are targeted by the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
before they are able to cause infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
. Those that escape the immune system's initial response, however, spread through intracellular mechanisms and are, therefore, guarded against circulating immune factors (AMI).
To invade, Listeria induces macrophage phagocytic uptake by displaying D-galactose in their teichoic acid
Teichoic acid
Teichoic acids are bacterial polysaccharides of glycerol phosphate or ribitol phosphate linked via phosphodiester bonds.-Location and structure:...
s that are then bound by the macrophage
Macrophage
Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...
's polysaccharide
Polysaccharide
Polysaccharides are long carbohydrate molecules, of repeated monomer units joined together by glycosidic bonds. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure,...
receptors. Other important adhesins are the internalin
Internalin
Internalins are surface proteins found on Listeria monocytogenes. They exist in two known forms, InlA and InlB. They are used by the bacteria to invade mammalian cells via cadherins transmembrane proteins. The exact role of these proteins and their invasiveness in vivo is not completely understood...
s. Once phagocytosed, the bacterium is encapsulated by the host cell's acidic phagolysosome
Phagolysosome
A phagolysosome is the membrane-enclosed organelle which forms when a phagosome fuses with a lysosome. After fusion, the food particles or pathogens contained within the phagosome are usually digested by the enzymes contained within the lysosome. Phagolysosome formation follows phagocytosis...
organelle. Listeria, however, escapes the phagolysosome by lysing the vacuole's entire membrane with secreted hemolysin
Hemolysin
Hemolysins are exotoxins produced by bacteria that cause lysis of red blood cells in vitro. Visualization of hemolysis of red blood cells in agar plates facilitates the categorization of some pathogenic bacteria such as Streptococcus and Staphylococcus...
, now characterized as the exotoxin listeriolysin O. The bacteria then replicate inside the host cell's cytoplasm.
Listeria must then navigate to the cell's periphery to spread the infection to other cells. Outside the body, listeria has flagellar-driven motility, sometimes described as a "tumbling motility." However, at 37 °C, flagella cease to develop and the bacterium instead usurps the host cell's cytoskeleton
Cytoskeleton
The cytoskeleton is a cellular "scaffolding" or "skeleton" contained within a cell's cytoplasm and is made out of protein. The cytoskeleton is present in all cells; it was once thought to be unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton...
to move. Listeria, inventively, polymerizes an actin
Actin
Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
tail or "comet", from actin monomers in the host's cytoplasm with the promotion of virulence factor ActA. The comet forms in a polar manner and aids the bacteria's migration to the host cell's outer membrane. Gelsolin, an actin filament severing protein, localizes at the tail of listeria and accelerates the bacterium's motility. Once at the cell surface, the actin-propelled listeria pushes against the cell's membrane to form protrusions called filopods or "rockets". The protrusions are guided by the cell's leading edge to contact adjacent cells, which then engulf the listeria rocket and the process is repeated, perpetuating the infection. Once phagocytosed, the listeria is never again extracellular: it is an intracytoplasmic parasite like Shigella flexneri
Shigella flexneri
Shigella flexneri is a species of Gram-negative bacteria in the genus Shigella that can cause diarrhea in humans. There are several different serogroups of Shigella; S. flexneri belongs to group B. S. flexneri infections can usually be treated with antibiotics although some strains have become...
and Rickettsia
Rickettsia
Rickettsia is a genus of non-motile, Gram-negative, non-sporeforming, highly pleomorphic bacteria that can present as cocci , rods or thread-like . Being obligate intracellular parasites, the Rickettsia survival depends on entry, growth, and replication within the cytoplasm of eukaryotic host cells...
.
Epidemiology
The Center for Science in the Public InterestCenter for Science in the Public Interest
Center for Science in the Public Interest is a Washington, D.C.-based non-profit watchdog and consumer advocacy group focusing on nutritional education and awareness.-History and funding:...
has published a list of foods that have sometimes caused outbreaks of Listeria: hot dogs, deli meats, raw milk, cheeses (particularly soft-ripened cheeses like feta, Brie, Camembert, blue-veined, or Mexican-style “queso blanco”), raw and cooked poultry, raw meats, ice cream, raw vegetables, raw and smoked fish.
Cantaloupe
Cantaloupe
"Rockmelon" redirects here, for the band see Rockmelons. See also Cantaloupe .Cantaloupe refers to a variety of Cucumis melo, a species in the family Cucurbitaceae which includes nearly all melons and squashes. Cantaloupes range in size from...
has been implicated in an outbreak of listeriosis from a farm in Colorado
2011 United States listeriosis outbreak
The 2011 United States listeriosis outbreak is an ongoing widespread outbreak of Listeria monocytogenes food poisoning across 26 U.S. states that resulted from contaminated cantaloupes linked to Jensen Farms of Holly, Colorado. As of November 1, 2011, there have been 29 deaths and 139 total...
, and the Australian company GMI Food Wholesalers were fined AU$236,000 for providing Listeria monocytogenes contaminated chicken wraps to the airline Virgin Blue
Virgin Blue
Virgin Australia Airlines, formerly Virgin Blue Airlines, is Australia's second-largest airline as well as the largest by fleet size to utilise the Virgin brand. Now based in Bowen Hills, Brisbane, Queensland, Australia, the airline was co-founded by British businessman Sir Richard Branson and...
.
Prevention
Preventing listeria as a food illness requires effective sanitation of food contact surfaces. AlcoholAlcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
is an effective topical sanitizer against Listeria. Quaternary ammonium can be used in conjunction with alcohol as a food contact safe sanitizer with increased duration of the sanitizing action. Refrigerated foods in the home should be kept below 4 °C (39.2 °F) to discourage bacterial growth. Preventing listeriosis also can be done by carrying out an effective sanitation of food contact surfaces.
Treatment
Antibiotics effective against listeria species include ampicillinAmpicillin
Ampicillin is a beta-lactam antibiotic that has been used extensively to treat bacterial infections since 1961. Until the introduction of ampicillin by the British company Beecham, penicillin therapies had only been effective against Gram-positive organisms such as staphylococci and streptococci...
, vancomycin
Vancomycin
Vancomycin INN is a glycopeptide antibiotic used in the prophylaxis and treatment of infections caused by Gram-positive bacteria. It has traditionally been reserved as a drug of "last resort", used only after treatment with other antibiotics had failed, although the emergence of...
(unclear effectiveness), ciprofloxacin
Ciprofloxacin
Ciprofloxacin is a synthetic chemotherapeutic antibiotic of the fluoroquinolone drug class.It is a second-generation fluoroquinolone antibacterial. It kills bacteria by interfering with the enzymes that cause DNA to rewind after being copied, which stops synthesis of DNA and of...
, linezolid
Linezolid
Linezolid is a synthetic antibiotic used for the treatment of serious infections caused by Gram-positive bacteria that are resistant to several other antibiotics...
, azithromycin
Azithromycin
Azithromycin is an azalide, a subclass of macrolide antibiotics. Azithromycin is one of the world's best-selling antibiotics...
.
Mixtures of bacteriophages have also proven effective in the treatment of Listeria.
Research
Listeria is an opportunistic pathogen: It is most prevalent in the elderly, pregnant mothers, and AIDS patients. With improved healthcare leading to a growing elderly population and extended life expectancies for AIDS patients, physicians are more likely to encounter this otherwise-rare infection (only 7 per 1,000,000 healthy people are infected with virulent listeria each year). Better understanding the cell biology of Listeria infections, including relevant virulence factors, may lead to better treatments for listeriosis and other intracytoplasmic parasite infections. Researchers are now investigating the use of listeria as a cancer vaccine, taking advantage of its "ability to induce potent innate and adaptive immunity."See also
- 2008 Canadian listeriosis outbreak2008 Canadian listeriosis outbreakThe 2008 Canadian listeriosis outbreak was a widespread outbreak of listeriosis in Canada linked to cold cuts from a Maple Leaf Foods plant in Toronto, Ontario. 22 people died and there were 57 total confirmed cases.-Origin and spread:...
- 2011 United States listeria outbreak
- List of foodborne illness outbreaks
Sources
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External links
- Listeria genome at PATRIC, funded by the National Institute of Allergy and Infectious DiseasesNational Institute of Allergy and Infectious DiseasesThe National Institute of Allergy and Infectious Diseases is one of the 27 institutes and centers that make up the National Institutes of Health , an agency of the United States Department of Health and Human Services...