Bacillus cereus
Encyclopedia
Bacillus cereus is an endemic
, soil
-dwelling, Gram-positive, rod-shaped
, beta hemolytic
bacterium
. Some strains are harmful to humans and cause foodborne illness
, while other strains can be beneficial as probiotics for animals. It is the cause of "Fried Rice
Syndrome," as the bacteria is classically contracted from fried rice dishes that have been sitting at room temperature for hours (such as at a buffet
). B. cereus bacteria are aerobes, and like other members of the genus Bacillus
can produce protective endospore
s. Its virulence factors include cereolysin and phospholipase C
.
and Campylobacter
in the gut
, so its presence reduces the numbers of those microorganisms. In food animals such as chickens, rabbit
s and pig
s, some harmless strains of B. cereus are used as a probiotic
feed additive
to reduce Salmonella in the intestine
s and cecum
. This improves the animals' growth as well as food safety for humans who eat their meat.
, vomiting
and diarrhea
. Bacillus foodborne illnesses occur due to survival of the bacterial endospores when food is improperly cooked. Cooking temperatures less than or equal to 100 °C (212 °F) allows some B. cereus spores to survive. This problem is compounded when food is then improperly refrigerated
, allowing the endospores to germinate. Cooked foods not meant for either immediate consumption or rapid cooling and refrigeration should be kept at temperatures above 60 °C (140 °F). Germination and growth generally occurs between 10–50 °C (50–122 °F), though some strains are psychrotrophic
. Bacterial growth results in production of enterotoxin
s, one of which is highly resistant to heat and to pH
between 2 and 11; ingestion leads to two types of illness, diarrheal and emetic (vomiting) syndrome.
The diarrhetic syndromes observed in patients are thought to stem from the three toxins Hemolysin BL Hbl, Nonhemolytic Enterotoxin Nhe and Cytotoxin K CytK. The nhe/hbl/cytK genes are located on the chromosome of the bacteria. Transcription of these genes is controlled by PlcR. These genes occur as well in the toxonomically related B. thuringensis and B. anthracis. These enterotoxins are all produced in the small intestine of the host, thus thwarting the issue of digestion by host endogenous enzymes. The Hbl and Nhe toxins are pore-forming toxins closely related to ClyA of E. coli. The proteins exhibit a conformation known as "beta-barrel" that can insert into cellular membranes due to a hydrophobic exterior, thus creating pores with hydrophilic interiors. The effect is loss of cellular membrane potential
and eventually cell death. CytK is a pore-forming protein more related to other hemolysins.
It was previously thought that the timing of the toxin production might be responsible for the two different courses of disease, but in fact the emetic syndrome is caused by a toxin called cereulide that is found only in emetic strains and is not part of the "standard toolbox" of B. cereus. Cereulide contains 3 repeats of 4 amino acids (similar to Valinomycin
produced by Streptomyces griseus
) produced by nonribosomal peptide synthesis (NRPS)
. Cereulide is believed to activate 5-HT3 (serotonin
) receptors leading to increased afferent
vagus nerve stimulation
. It was shown independently by two research groups to be encoded on multiple plasmid
s: pCERE01 or pBCE4810. Plasmid pBCE4810 shares homology with the Bacillus anthracis
virulence plasmid pXO1, which encodes the anthrax toxin
. Periodontal isolates of B. cereus also possess distinct pXO1-like plasmids.
B. cereus is also known to cause chronic skin infections that are difficult to eradicate though less aggressive than necrotizing fasciitis
. B. cereus can also cause keratitis
.
It recommended as pathogenic microflora in pharmaceutical oral products in Brazilian Phamacopaeia.
, the diagnosis of B. cereus can be confirmed by the isolation of more than 105 B. cereus organisms per gram from epidemiologically implicated food, but such testing is often not done because the illness is relatively harmless and usually self-limiting.
Endemic (epidemiology)
In epidemiology, an infection is said to be endemic in a population when that infection is maintained in the population without the need for external inputs. For example, chickenpox is endemic in the UK, but malaria is not...
, soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
-dwelling, Gram-positive, rod-shaped
Bacillus
Bacillus is a genus of Gram-positive, rod-shaped bacteria and a member of the division Firmicutes. Bacillus species can be obligate aerobes or facultative anaerobes, and test positive for the enzyme catalase. Ubiquitous in nature, Bacillus includes both free-living and pathogenic species...
, beta hemolytic
Hemolysis (microbiology)
Hemolysis is the breakdown of red blood cells. The ability of bacterial colonies to induce hemolysis when grown on blood agar is used to classify certain microorganisms. This is particularly useful in classifying streptococcal species...
bacterium
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...
. Some strains are harmful to humans and cause foodborne illness
Foodborne illness
Foodborne illness is any illness resulting from the consumption of contaminated food, pathogenic bacteria, viruses, or parasites that contaminate food, as well as chemical or natural toxins such as poisonous mushrooms.-Causes:Foodborne illness usually arises from improper handling, preparation, or...
, while other strains can be beneficial as probiotics for animals. It is the cause of "Fried Rice
Fried rice
Fried rice is a popular component of Asian cuisine, especially Chinese food. It is made from steamed rice stir-fried in a wok, often with other ingredients such as eggs, vegetables, and meat. It is sometimes served as the penultimate dish in Chinese banquets...
Syndrome," as the bacteria is classically contracted from fried rice dishes that have been sitting at room temperature for hours (such as at a buffet
Buffet
A buffet is a system of serving meals in which food is placed in a public area where the diners generally serve themselves. Buffets are offered at various places including hotels and many social events...
). B. cereus bacteria are aerobes, and like other members of the genus Bacillus
Bacillus
Bacillus is a genus of Gram-positive, rod-shaped bacteria and a member of the division Firmicutes. Bacillus species can be obligate aerobes or facultative anaerobes, and test positive for the enzyme catalase. Ubiquitous in nature, Bacillus includes both free-living and pathogenic species...
can produce protective endospore
Endospore
An endospore is a dormant, tough, and temporarily non-reproductive structure produced by certain bacteria from the Firmicute phylum. The name "endospore" is suggestive of a spore or seed-like form , but it is not a true spore . It is a stripped-down, dormant form to which the bacterium can reduce...
s. Its virulence factors include cereolysin and phospholipase C
Phospholipase C
Phosphoinositide phospholipase C is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. In general, this enzyme is denoted as Phospholipase C, although three other families of phospholipase C enzymes have been identified in bacteria and in...
.
Symbiosis
B. cereus competes with other microorganisms such as SalmonellaSalmonella
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...
and Campylobacter
Campylobacter
Campylobacter is a genus of bacteria that are Gram-negative, spiral, and microaerophilic. Motile, with either unipolar or bipolar flagella, the organisms have a characteristic spiral/corkscrew appearance and are oxidase-positive. Campylobacter jejuni is now recognized as one of the main causes...
in the gut
Gut (zoology)
In zoology, the gut, also known as the alimentary canal or alimentary tract, is a tube by which bilaterian animals transfer food to the digestion organs. In large bilaterians the gut generally also has an exit, the anus, by which the animal disposes of solid wastes...
, so its presence reduces the numbers of those microorganisms. In food animals such as chickens, rabbit
Rabbit
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...
s and pig
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
s, some harmless strains of B. cereus are used as a probiotic
Probiotic
Probiotics are live microorganisms thought to be beneficial to the host organism. According to the currently adopted definition by FAO/WHO, probiotics are: "Live microorganisms which when administered in adequate amounts confer a health benefit on the host"...
feed additive
Feed additive
A feed additive is a vitamin for farm animals that can't get enough nutrients from regular meals that the farmers provide. In some cases if an animal does not have some type of feed in its diet it may not grow properly...
to reduce Salmonella in the intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
s and cecum
Cecum
The cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...
. This improves the animals' growth as well as food safety for humans who eat their meat.
Pathogenesis
B. cereus is responsible for a minority of foodborne illnesses (2–5%), causing severe nauseaNausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
, vomiting
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...
and diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
. Bacillus foodborne illnesses occur due to survival of the bacterial endospores when food is improperly cooked. Cooking temperatures less than or equal to 100 °C (212 °F) allows some B. cereus spores to survive. This problem is compounded when food is then improperly refrigerated
Refrigeration
Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...
, allowing the endospores to germinate. Cooked foods not meant for either immediate consumption or rapid cooling and refrigeration should be kept at temperatures above 60 °C (140 °F). Germination and growth generally occurs between 10–50 °C (50–122 °F), though some strains are psychrotrophic
Psychrotrophic bacteria
Psychrotrophic bacteria are bacteria that are capable of surviving or even thriving in a cold environment. They can be found in soils, in surface and deep sea waters, in Antarctic ecosystems, and in foods....
. Bacterial growth results in production of enterotoxin
Enterotoxin
An enterotoxin is a protein toxin released by a microorganism in the intestine. Enterotoxins are chromosomally encoded exotoxins that are produced and secreted from several bacterial organisms. They are often heat-stable, and are of low molecular weight and water-soluble...
s, one of which is highly resistant to heat and to pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
between 2 and 11; ingestion leads to two types of illness, diarrheal and emetic (vomiting) syndrome.
- The diarrheal type is associated with a wide-range of foods, has an 8- to 16.5-hour incubation timeIncubation periodIncubation period is the time elapsed between exposure to a pathogenic organism, a chemical or radiation, and when symptoms and signs are first apparent...
and is associated with diarrhea and gastrointestinal pain. Also known as the long-incubation form of B. cereus food poisoning, it might be difficult to differentiate from poisoning caused by Clostridium perfringensClostridium perfringensClostridium perfringens is a Gram-positive, rod-shaped, anaerobic, spore-forming bacterium of the genus Clostridium. C. perfringens is ever present in nature and can be found as a normal component of decaying vegetation, marine sediment, the intestinal tract of humans and other vertebrates,...
. - The emetic form is commonly caused by rice that is not cooked for a time and temperature sufficient to kill any spores present, then improperly refrigerated. It can produce a toxinToxinA toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...
, cereulide, which is not inactivated by later reheating. This form leads to nausea and vomiting 1–5 hours after consumption. It can be difficult to distinguish from other short-term bacterial foodborne pathogens such as Staphylococcus aureusStaphylococcus aureusStaphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...
.
The diarrhetic syndromes observed in patients are thought to stem from the three toxins Hemolysin BL Hbl, Nonhemolytic Enterotoxin Nhe and Cytotoxin K CytK. The nhe/hbl/cytK genes are located on the chromosome of the bacteria. Transcription of these genes is controlled by PlcR. These genes occur as well in the toxonomically related B. thuringensis and B. anthracis. These enterotoxins are all produced in the small intestine of the host, thus thwarting the issue of digestion by host endogenous enzymes. The Hbl and Nhe toxins are pore-forming toxins closely related to ClyA of E. coli. The proteins exhibit a conformation known as "beta-barrel" that can insert into cellular membranes due to a hydrophobic exterior, thus creating pores with hydrophilic interiors. The effect is loss of cellular membrane potential
Membrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
and eventually cell death. CytK is a pore-forming protein more related to other hemolysins.
It was previously thought that the timing of the toxin production might be responsible for the two different courses of disease, but in fact the emetic syndrome is caused by a toxin called cereulide that is found only in emetic strains and is not part of the "standard toolbox" of B. cereus. Cereulide contains 3 repeats of 4 amino acids (similar to Valinomycin
Valinomycin
Valinomycin is a dodecadepsipeptide antibiotic.Valinomycin is obtained from the cells of several Streptomyces strains, among which "S. tsusimaensis" and S. fulvissimus....
produced by Streptomyces griseus
Streptomyces griseus
Streptomyces griseus is a member bacterial species of the genus Streptomyces and are commonly found in soil. A few strains have been also reported from deep sea sediments. These are Gram positive bacterium with high GC content. Along with most other streptomycetes S...
) produced by nonribosomal peptide synthesis (NRPS)
Nonribosomal peptide
Nonribosomal peptides are a class of peptide secondary metabolites, usually produced by microorganisms like bacteria and fungi. Nonribosomal peptides are also found in higher organisms, such as nudibranchs, but are thought to be made by bacteria inside these organisms...
. Cereulide is believed to activate 5-HT3 (serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
) receptors leading to increased afferent
Afferent
Afferent is an anatomical term with the following meanings:*Conveying towards a center, for example the afferent arterioles conveying blood towards the Bowman's capsule in the Kidney. Opposite to Efferent.*Something that so conducts, see Afferent nerve fiber...
vagus nerve stimulation
Vagus nerve stimulation
Vagus nerve stimulation is an adjunctive treatment for certain types of intractable epilepsy and treatment-resistant depression.- Mechanism of action :...
. It was shown independently by two research groups to be encoded on multiple plasmid
Plasmid
In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...
s: pCERE01 or pBCE4810. Plasmid pBCE4810 shares homology with the Bacillus anthracis
Bacillus anthracis
Bacillus anthracis is the pathogen of the Anthrax acute disease. It is a Gram-positive, spore-forming, rod-shaped bacterium, with a width of 1-1.2µm and a length of 3-5µm. It can be grown in an ordinary nutrient medium under aerobic or anaerobic conditions.It is one of few bacteria known to...
virulence plasmid pXO1, which encodes the anthrax toxin
Anthrax toxin
Anthrax toxin is a three-protein exotoxin secreted by virulent strains of the bacterium, Bacillus anthracis--the causative agent of anthrax. The toxin was first discovered by Harry Smith in 1954. Anthrax toxin is composed of a cell-binding protein, known as protective antigen , and two enzyme...
. Periodontal isolates of B. cereus also possess distinct pXO1-like plasmids.
B. cereus is also known to cause chronic skin infections that are difficult to eradicate though less aggressive than necrotizing fasciitis
Necrotizing fasciitis
Necrotizing fasciitis , commonly known as flesh-eating disease or Flesh-eating bacteria syndrome, is a rare infection of the deeper layers of skin and subcutaneous tissues, easily spreading across the fascial plane within the subcutaneous tissue.Necrotizing fasciitis is a quickly progressing and...
. B. cereus can also cause keratitis
Keratitis
Keratitis is a condition in which the eye's cornea, the front part of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves impaired eyesight.-Types:...
.
It recommended as pathogenic microflora in pharmaceutical oral products in Brazilian Phamacopaeia.
Diagnosis
In case of foodborne illnessFoodborne illness
Foodborne illness is any illness resulting from the consumption of contaminated food, pathogenic bacteria, viruses, or parasites that contaminate food, as well as chemical or natural toxins such as poisonous mushrooms.-Causes:Foodborne illness usually arises from improper handling, preparation, or...
, the diagnosis of B. cereus can be confirmed by the isolation of more than 105 B. cereus organisms per gram from epidemiologically implicated food, but such testing is often not done because the illness is relatively harmless and usually self-limiting.
External links
- Bacillus cereus genomes and related information at PATRIC, a Bioinformatics Resource Center funded by NIAID