An Overview of Bacillus cereus
An Overview of Bacillus cereus

Bacteriology

An Overview of Bacillus cereus

Colonies from B. cereus initially isolated from an agar plate that was left exposed to air in the cow shed. In the...

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This article writter by MN Editors on January 24, 2022

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Domain: Bacteria
Phylum:“Firmicutes”
Class: Bacilli
Order: Bacillales
Family: Bacillaceae
Genus: Bacillus
Species: B. cereus

Colonies from B. cereus initially isolated from an agar plate that was left exposed to air in the cow shed. In the year 2010, the review of warning letters from the US Food and Drug Administration for pharmaceutical manufacturing facilities that addressed microbiological contamination showed that the most frequent contamination to be found was B. cereus.

A variety of newly discovered enzymes were found In B. cereus and other B. cereus species, including AlkC and AlkD Both of them are involved in the repair of DNA.

Bacillus cereus Definition

Bacillus cereus (B. cereus) is one of the foodborne pathogen which produces toxins, which can cause two forms of gastrointestinal disease that include an”emetic” (vomiting) syndrome as well as the diarrhoeal condition. When the emetic toxins (cereulide) is created within the food that is consumed, vomiting may occur after the consumption of the food contaminated with the toxin. The diarrhoeal disorder occurs when enterotoxins are released into the intestine after the eating food that is contaminated with B. cereus.

Habitat of Bacillus cereus

  • Bacillus cereus has been isolated from the soil, vegetable cereals, milk spice, rice, fried cooked meats and poultry as well as desserts, soups and soups.
  • It can also be present in mashed potatoes, apple stew, beef stew hot chocolates that are available in vending machines and in other food handling facilities.
  • It was in 1887 that B. cereus had been removed from the air within a cowshed Frankland in 1887, as was Frankland.
  • It is an saprophytic species of Bacillus.
  • Vegetative cells as well as spores are found throughout the world.
  • It is an opportunistic pathogen that affects patients with immunocompromised conditions and, sometimes, the pathogens that affect humans.
  • It is not considered to be a normal human flora but it may transiently infiltrate the skin, the gastrointestinal tract or respiratory tracts.
  • Endospores have a higher resistance to chemical and physical agents like heat, cold, desiccationand disinfection, radiation and other toxins.
  • It can grow regardless of whether or out of oxygen.
  • It is in contact with other microorganisms of the rhizosphere, which is the area that surrounds roots of plants.
  • It’s also found in the microflora of invertebrates. It is also an arthropod symbiont in the intestinal tract which exhibit filamentous growth in roaches, termites, and roaches.
  • Bacillus cereus can’t be killed by alcohol. In fact, they’ve been found to live in distilled liquors and alcohol-soaked swabs as well as pads in such a way that they create an infection.
  • A positive test for B. cereus on the stool of a patient does not necessarily mean that there is the diagnosis for B. cereus since bacteria can be present in normal stool specimens A concentration of more than 105 bacteria per milligram of food is to be a diagnostic.

Morphology of Bacillus cereus

  • Bacillus cereus is a rod-shaped gram-positive Bacillus with square-ended ends.
  • Sometimes, they appear gram-variable or even gram negative with the passage of time.
  • They can be single rods or occur as short chain.
  • Clear cut junctions between chains’ members are readily discernible.
  • The staining of tissue sections can appear long and spongy.
  • They can be straight or curving.
  • They are not sealed.
  • It has spores that have central spores.
  • Spores appear oval (ellipsoidal) and are not swelling the mother cell. They are they do not form in the blood of animals and tissues, or in aerobic cultures.
  • It’s 1×3-4 um in the size.
  • It’s fluid and flagellated with peritrichous flagella.
  • It is motile due to two kinds of motility: swimming and swarming.
  • Endospores can withstand prolonged exposure to air and other harsh environmental conditions.
  • Beta-hemolytic bacterium which can cause foodborne illness.
  • The virulence factors are the phospholipase and cerolysin.

Genome Structure

  • The circular chromosome has 5,411,809 nt of length.
  • It is composed of the following proteins: 5481 genes that code structural RNA, 147 structural RNA as well as 5366 operons of RNA.
  • The plasmid ranges from between 5 and 500 kb in size.

Cultural Characteristics of Bacillus cereus

  • The majority of Bacillus spp are easily grown on peptone or nutrient agar media.
  • The optimal temperature for growth can vary from 20degC to 40degC typically 37degC.
  • B. cereus has mesophilic characteristics, and in a position to adapt to a vast variety of conditions.
  • In Nutrient Agar when it is at 37degC it creates large (2-5 millimeters) grey-white colony granular with edges that are less wavy and a less membranous appearance.
  • On 5% of sheep blood assay in 37degC, B. cereus colonies are big and feathery. They are dull gray, granular expanding colonies, and opaque , with rough matted surfaces as well as irregularly shaped perimeters.
  • On the blood agar, there is beta-hemolytic.
  • Colony perimeters vary and reflect the pattern of swarming at the site of inoculation. This could be because of B. cereus’s swarming.
  • In some cases the formation of smooth colonies occurs by themselves or in the midst the rough colonies.
  • If separated from the initial inoculum colony walls are smooth and covered by a uniform layer of beta-hemolysis, which frames the centrally placed colony.
  • The MYP Agar is the most commonly used media used for plating B. cereus however, it does not have a high degree of selectivity, which means that background flora isn’t affected and may obscure any presence of B. cereus. The B. cereus colonies tend to be lecithinase positive and mannitol negative on MYP Agar.
  • Bacara is a chromogenic, selective and differential agar that encourages the development and recognition of B. cereus while limiting the expansion of background the flora. Bacillus cereus colonies change color from pink to orange with an transparent shimmering halo.
  • The chromogenic agar was recommended for the enumeration of B. cereus. B. cereus species to replace MYP. The typical colonies develop as pink-orange uniform colonies that are surrounded by a precipitation zone.

Ecology of Bacillus cereus

Like many Bacilli of the world, the main environment for Bacillus cereus is the land. Together with Arbuscular mycorrhiza (and Rhizobium leguminosarum in clover) they are able to regenerate soils made of heavy metals by increasing the phosphorus, nitrogen and potassium levels in specific plants.

B. cereus can compete with other microorganisms like Salmonella as well as Campylobacter within the gut. its presence can reduce the number of microorganisms. In animals that eat food, such as rabbits, chickens and pigs, certain harmless species from B. cereus have been utilized as a probiotic additive to feed to help reduce Salmonella in the animal’s digestive tract and cecum. This helps improve the animal’s development, and the food safety for humans who consume these animals. B. cereus is a parasite that can infect Codling moth larvae.

B. cereus as well as the other members of Bacillus aren’t readily killed by alcohol, but they are recognized to infect distilled liquors and alcohol-soaked swabs as well as pads in sufficient numbers to cause an infection. Certain varieties from B. cereus can produce cereins, bacteriocins that are active against various B. cereus species, or different Gram-positive bacteria.

Characteristics of B. cereus

Test type Test Characteristics
Colony characters Size Medium
Type Round
Color Whitish
Shape Convex
Morphological characters Shape Rod
Physiological characters Motility +
Growth at 6.5% NaCl +
Biochemical characters Gram’s staining +
Oxidase +
Catalase +
Oxidative-Fermentative Fermentative
Motility +
Methyl Red
Voges-Proskauer +
Indole
H2S Production
Urease V
Nitrate reductase +
β-Galactosidase
Hydrolysis of Gelatin +
Aesculin +
Casein +
Tween 40 +
Tween 60 +
Tween 80 +
Acid production from Glycerol +
Galactose V
D-Glucose +
D-Fructose +
D-Mannose
Mannitol +
N-Acetylglucosamine +
Amygdalin +
Maltose +
D-Melibiose +
D-Trehalose +
Glycogen +
D-Turanose V

Pathogenicity and Virulence factors of Bacillus cereus

B. cereus has been often linked to food poisoning, however, it can cause post-traumatic ophthalmitis that demands prompt, aggressive treatment locally. The organism is prevalent in the natural environment and is present in the majority of raw foods and cereals, particularly rice. Gastroenteritis is caused through B. cereus can be caused by two enterotoxins.

The heat-stable, proteolysis-resistant enterotoxin causes the emetic form of the disease. The mechanism by which it acts the enterotoxin that is heat-stable is not known. The emetic version is characterized by vomiting, nausea abdominal cramps, nausea and sometimes diarrhea. It is self-limiting, and recovery occurs in less than 24 hours. Enterotoxin that is heat-labile is the cause of diarrheal forms of the disease. Each triggers the adenylate-cyclase-cyclic aden monophosphate system of intestinal epithelial cells. This leads to a plethora of watery diarrhea.

The diarrheal type has an incubation time of 1 to 24 hours. It is characterized as a frequent diarrhea accompanied by abdominal cramps and pain. Fever and vomiting are not common. B. cereus is one of the frequently identified kind from Bacillus in opportunistic diseases, including endocarditis after a traumatic injury, posttraumatic eye infections and the bacteremia. The pathogenesis behind B. cereus eye infections is not fully understood.

Three toxicants have been implicated. they include necrotic toxin (a thermo-labile form of enterotoxin) cereolysin, necrotic toxin, and the phospholipase C (a powerful lecithinase). It is possible that the fast destruction of the eye typical in B. cereus-related infections arises from the interaction between these toxins with other unknown elements. Bacillus species are able to colonize the skin for a short time and be found as small substances in blood culture.

If there is an intravascular foreign body but these microorganisms could be the cause of chronic bacteremia and symptoms of sepsis (i.e. symptoms of hypotension, chills, fever shock, etc.). Infections at other sites are uncommon and are usually associated with those who abuse intravenous drugs or patients with immunocompromised conditions.

Clinical manifestation of Bacillus cereus

A. Food poisoning

Two types of food poisoning are vomiting disorder (emetic type) and diarrheal illness (diarrheal type).

1. Emetic form

The emetic version of the disease is caused by the consumption of rice that has been contaminated. The majority of bacteria die in the cooking process that begins the rice, however the heat-resistant spores persist. If the rice cooked is not refrigerated after cooking, the germinating spores will grow, and the bacteria may grow quickly. The heat-stable enterotoxin released does not get rid of itself when the rice is heated. The emetic variant that is the result of this disease intoxication triggered by intake of the enterotoxin but rather than the bacteria. Therefore, the time of incubation after eating the rice that has been contaminated is brief (1 or 6 hours) and the duration of illness is also minimal (less than 24 hours). The symptoms include nausea, vomiting as well as abdominal cramps. In general, diarrhea and fever are absent.

2. Diarrheal form

The diarrheal variant is a form of B. cereus poisoning in food is an actual disease that is caused by the ingestion of bacteria that are present in meat vegetables, sauces, or other food items. There is a lengthy incubation time, where the organism grows within the intestinal tract of the patient and the release of enterotoxin that is heat-labile follows. Enterotoxin is the cause of the frequent diarrhoea, nausea and abdominal cramps.

B. Eye infections

B. cereus Ocular infections typically occur following traumatizing, penetrating wounds to the eye caused by a soil or other object that is contaminated. This includes severe keratitis as well as endophthalmitis.

C. Other infections

B. cereus is also linked to localized infections, like wound infections as well as with systemic infections, such as endocarditis, central nervous system diseases osteomyelitis and pneumonia. The presence of medical devices or intravenous drug use can lead to the occurrence of these infections.

Laboratory Diagnosis of Bacillus cereus

SPECIMENS: Faeces, vomitus, remaining food (if any), eye specimen (corneal swab)

DIRECT DETECTION METHODS

  1. Microscopically, these organisms are seen as massive gram-positive rods, in pairs, singles or serpentine that have the ends shaped like squares after staining with Gram.
  2. Endospores are an uncolored oval or a round area in the center of the cell. Spores appear rectangular (ellipsoidal) and do not show an expansion of the mother cell.
DIRECT DETECTION METHODS
DIRECT DETECTION METHODS

CULTURE

  1. Growth on the 5% sheep blood agar and chocolate agar. Also and routine blood culture media and nutritional broths.
  2. Growth can be observed within 24 hours after the incubation of media at 35 deg C and in ambient air or in 5 percent CO2 (CO2).
  3. Colony characteristics on blood agar that is large feathery, spread dull, gray colonies that are spreading, granular and opaque with rough matted surfaces and irregular borders and beta-hemolytic.
  4. Bacillus cereus can be separated from feces using specific media like MYPA (mannitol eggs, egg yolks, polymyxin Agar, phenol red, and), PEMBA (polymyxin, egg yolk, mannitol bromothymol blue Agar).
  5. These media benefit from the phospholipase C positive reaction that occurs on egg yolk agar. There is no acid production from mannitol, and the addition of polymyxin and pyruvate as selective agents.

BIOCHEMICAL ANALYSIS

  • Catalase: positive
  • Oxidase: negative
  • OF test: fermentative
  • Indole: negative
  • Methyl red: positive
  • Vogues proskauer: positive
  • Glucose: fermentative, production of acid
  • Sucrose: fermentative, production of acid
  • Lactose: no fermentation
  • Starch hydrolysis: positive
  • Nitrate reduction: positive
  • Gelatin hydrolysis: positive
  • Spore staining: endospore-forming bacteria
  • Motility: motile

SERODIAGNOSIS  

  1. There are serologic methods available to identify B. cereus toxins in feces and in food.
  2. Microslide gel diffusion tests are commonly used as a detection method.

MOLECULAR METHOD

  1. The potential toxigenicity is present in B. cereus strains the genes that encode emetic-toxin-cereulide (ces) as well as Enterotoxins (nhe, hbl and CytK) can be evaluated using multiplex PCR.

Treatment of Bacillus cereus

  • People suffering from B. cereus-related food poisoning need only support.
  • Oral rehydration and, sometimes intravenous fluid and electrolyte replacement for those suffering from severe dehydration are recommended. Antibiotics are not recommended.
  • Patients with the invasive illness require treatment with antibiotics. Bacillus cereus can be affected by clindamycin vancomycin, erythromycin, aminoglycosides, as well as Tetracycline. It is intolerant to trimethoprim and penicillin.

Prevention and Control of Bacillus cereus

  • The intoxication of vomiting and diarrhea due to this organism are easily prevented by proper food handling procedures.
  • Food items such as vegetables and meat shouldn’t be stored at temperatures that range from 10 and 45 degrees Celsius for extended periods and the rice stored for a night or more after cooking must be kept refrigerated, not stored at the room temperature.
  • The prevention of infection for patients who have undergone surgery or those with immunocompromised conditions or are predisposed to infection relies on the quality of care.

What are the symptoms of B. cereus food poisoning?

There are two primary kinds of B. cereus that can cause food safety issues. The first is responsible for diarrhoea (diarrhoeal-type) and the second one can cause nausea (vomiting-type).

The diarrhoeal type in B. cereus is a harmful substances within the small intestinal. This means that one is susceptible to suffering from diarrhoea, if they consume food items that contain high levels of the bacteria or the spores (which could later transform to bacteria).

Spores from this type of bacteria are found in various types of food like milk and meat. Researchers have discovered that certain foods like soups, sauces or salads (with raw vegetables) typically contain an abundance of B. cereus. Dry plant products, like spices, herbs and cereals also have various levels of the bacteria. If these items are added to other kinds of food items or are made into drinking water, the spores can become bacteria and then grow in large quantities if the food is not consumed in a timely manner.

The vomiting form that is a result of B. cereus can cause toxic substances in food. It is the reason that a person might experience nausea, vomiting and abdominal cramps when he or she consumes food that is contaminated. This kind of bacteria is typically associated with foods high in starch, like pasta, rice and noodles. The bacteria are able to multiply quickly and create toxins in foods if they are kept within”the “temperature dangerous zone” for a long time. In this scenario the quantity of toxins consumed will affect intensity of the symptoms experienced by the affected person.

For healthy individuals generally, they only experience mild discomfort and generally get better on their own within one day.

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