Bacillus cereus characteristics, morphology, habitat

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Jonah Lester
Bacillus cereus characteristics, morphology, habitat

Bacillus cereus It is a bacterium belonging to the genus Bacillus that is capable of producing toxins. Despite having been studied frequently, it is not yet fully known, and certain aspects remain to be discovered..

It has been possible to isolate specimens of Bacillis cereus in a multitude of environments such as soil, water, certain plants and even in the intestines of some animals. From this it can be deduced that this bacterium is capable of surviving under very diverse and wide conditions..

Source: By Mogana Das Murtey and Patchamuthu Ramasamy ([1]) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

The importance of studying this bacterium is that it is associated with certain pathologies, mainly of the gastrointestinal system. Thanks to its ability to survive, it can prevail in food, even after cooking and infect humans..

Although infections caused by it generally have a good outcome, fatal cases have been described. Those most affected are immunosuppressed people, whose immune system cannot effectively cope with these infections.

Article index

  • 1 Taxonomy
  • 2 Features
    • 2.1 It is a gram positive bacteria
    • 2.2 It is facultative anaerobic
    • 2.3 It is mesophilic
    • 2.4 Has a varied metabolism
    • 2.5 It is catalase positive
    • 2.6 Survives in a wide pH range
    • 2.7 It is a beta hemolytic bacterium
    • 2.8 Produces spores
  • 3 Morphology
  • 4 Habitat
  • 5 Diseases it produces
  • 6 Symptoms generated by Bacillis cereus
    • 6.1 Emetic syndrome
    • 6.2 Diarrheal syndrome
    • 6.3 Keratitis
    • 6.4 Panophthalmitis
    • 6.5 Endophthalmitis
  • 7 Bacillus cereus in food
  • 8 References

Taxonomy

In order to elucidate the characteristics and biological behavior of an organism, it is necessary to know its taxonomy. In the case of  Bacillus cereus,  is the next:

Domain: Bacteria

Phylum: Firmicutes

Class: Bacilli

Order: Bacillales

Family: Bacillaceae

Gender: Bacillus

Species: B. cereus

Characteristics

Bacillus cereus colonies on Columbia blood agar. Source: commons.wikimedia.org

Bacillus cereus is a bacterium of medical importance, due to the pathogenic effect of the toxins it produces. Among its most outstanding biological characteristics are:

It is a gram positive bacteria

Crops Bacillus cereus when subjected to the Gram staining process, they adopt a violet coloration. These are indisputable evidence of the presence of peptidoglycan in its cell wall, in which particles of the dye are trapped..

It is facultative anaerobic

Bacillus cereus can thrive in environments that are rich in oxygen, as well as in the absence of oxygen. Thanks to this, it is able to adapt to a wide variety of environments..

However, the type of habitat in which this microorganism best thrives is one that has oxygen. This is so for two reasons. The first one is that it requires oxygen to generate one of the two types of toxin it produces (emetics).

The second reason is that it has been experimentally shown that in the absence of oxygen the growth rate of this bacterium is reduced..

It is mesophilic

A mesophilic organism is one that develops optimally and efficiently in intermediate temperature ranges. In the case of Bacillus cereus, optimal growth temperature range is 30 ° C to 40 ° C.

Has a varied metabolism

Depending on the environmental conditions and the availability of nutrients, the Bacillus cereus can ferment various types of compounds. These include glucose, glycerol, salicin, and sucrose..

In addition to this, it is capable of metabolizing nitrates, transforming them into nitrites..

It is catalase positive

The Bacillus cereus has the enzyme catalase, which allows it to break down the hydrogen peroxide molecule in water and oxygen.

Survives in a wide pH range

PH is a parameter that refers to the degree of acidity or alkalinity. In the case of bacteria Bacillus cereus, can survive in environments whose pH is between 4.9 and 9.3.

This means that it adapts easily to slightly acidic and slightly alkaline environments. At a neutral pH they are effectively maintained.

It is a beta hemolytic bacteria

Bacillus cereus It is a bacterium that has the ability to produce hemolysis in erythrocytes. This can be evidenced by performing a culture on agar medium enriched with blood..

Produces spores

Spores are cells from which new bacteria can be generated. They constitute a kind of stationary phase in the life cycle of the Bacillus cereus.

The spores of this bacterium are characterized by being highly resistant to environmental changes, as well as physical factors such as gamma radiation..

Morphology

The Bacillus cereus it is a typical bacterium of the group of bacilli, with its characteristic rod-like shape with square ends. In crops they can be seen as straight or slightly curved bars.

They can also be individually or forming short chains. The average size of each bacterial cell is 1 x 3-4 microns and they have flagella uniformly distributed throughout their surface..

From a genetic point of view, they contain a single circular chromosome that has 5481 genes, which in turn encode a total of 5234 proteins.

Habitat

One of the most outstanding aspects of the Bacillus cereus it is its ubiquity. This means that it can be found in a wide variety of environments. All this thanks to its ability to survive in various environmental conditions of pH and temperature..

Through various studies it has been possible to isolate strains of this bacterium both in polar soils and in tropical places, which confirms its ability to colonize a diversity of environments..

They can be found in soils, plants, mineral waters, sediments, and even dust.

Diseases it produces

The Bacillus cereus it is a pathogenic bacterium that can produce numerous pathologies in humans: infections in the gastrointestinal tract and outside of it, as well as, in extreme cases, systemic infections.

This bacterium produces two types of toxins: cereulide and diarrhea. Each type of toxin has specific effects.

The gastrointestinal infections caused by this bacterium are:

Emetic syndrome: it is caused by cereulide toxin and is produced by ingesting food contaminated with it. Its incubation period is 1 to 5 hours.

Diarrheal syndrome: originates from the ingestion of spores that later develop in the small intestine. The incubation period is 1 to 24 hours.

At the level of the eyeball, the bacteria generate the following infections:

Keratitis: infection of the outermost layer of the eye, the cornea.

Panophthalmitis: inflammation that affects all structures of the eye. It can also affect the surrounding structures..

Endophthalmitis: infection that damages all layers of the eye. It is limited only to this.

Symptoms generated by Bacillis cereus

Emetic syndrome

  • Sickness
  • Repetitive vomiting
  • General discomfort.
  • In some cases there may be diarrhea and abdominal pain.
Source: Pixabay.com

Diarrheal syndrome

  • Profuse watery diarrhea
  • Abdominal pain
  • Rectal tenesmus.

Occasionally there may be a fever.

Keratitis

  • Eye pain
  • Tearing or discharge
  • Progressive loss of vision
  • Excessive sensitivity to light.

Panophthalmitis

  • Headache
  • Peri orbital pain
  • Redness
  • Swelling.

Endophthalmitis

  • Decreased vision
  • Edema around the eye
  • Eye pain
  • Redness of the sclera
  • Sensitivity to light.

It is important to be aware of any of these symptoms so that you can treat them in time. The progression of these infections can have permanent, long-term, as well as fatal consequences, especially when they develop in children..

Bacillus cereus in food

Although it is not the only foodborne pathogen, B. cereus it is responsible for most foodborne illness outbreaks. In recent decades, the total number of these diseases has had a growing trend worldwide.

The disease known as fried rice syndrome is an emetic syndrome caused by B. cereus. The usual cause is boiled rice that has been kept for long periods at room temperature and then quickly fried before serving..

Bacillus cereus It is the third responsible for diseases due to contaminated meat, after staphylococci and salmonella. The bacteria is also present in some spices, so its use in meats increases the risk of poisoning.

Raw milk can be contaminated by B. cereus. Because its spores resist pasteurization, it can also be present in pasteurized milk and various dairy derivatives..

Other foods that have been found to be contaminated with B. cereus include mixes for desserts, baby foods, precooked foods, seafood, cocoa, chocolate, legumes, fresh vegetables, cereals and their derivatives.

References

  1. American Association for Pediatric Ophthalmology and Strabismus. Retrieved from aapos.org.
  2. Bacillus cereus. Retrieved from microbewiki.kenyon.edu.
  3. Brooks G., Carroll K., Butel J., Morse S., Mietzner T. Medical Microbiology. 25th edition. Mc Graw Hill Interamericana. 2010.
  4. Cunningham, E. Endophthalmitis. Retrieved from msdmanuals.com
  5. Dierick, K., Van Coillie, E., Swiecicka, I., Meyfroidt, G., Devlieger, H., Meulemans, A., Hoedemaekers, G., Fourie, L., Heyndrickx, M. and Mahillon, J. (2005, August). Fatal Family Outbreak of Bacillus cereus- Associated Food Poisoning. Journal of Clinical Microbiology. 43 (8). 4277-4279.
  6. Drobnieweski, F. (1993, October). Bacillus cereus and related species. Clinical Microbiology Reviews. 6 (4). 324-338.
  7. Kotiranta, A., Lounatmaa, K., Haapasalo, M. (2000, February). Epidemiology and pathogenesis of Bacillus cereus infections. Microbes and infection. 2 (2). 189-198
  8. Kumar, N., Garg, N., Kumar, N., Van Wagoner. (2014, September). Bacillus cereus panophthalmitis associated with injection drug use. International Journal of Infectious Diseases. 26. 165-166.
  9. Ministry of Social Protection of Colombia. (2011). Risk profile Bacillus cereus in non-industrialized ready-to-eat foods. Recovered from: minsalud.gov.co
  10. Morphology of Bacillus cereus. Obtained from microbenotes.com
  11. Pan American Health Organization. Biological Hazards. Retrieved from paho.org
  12. Pan American Health Organization. Food poisoning due to Bacillus cereus. Retrieved from new.paho.org
  13. Realpe, M.,., Hernández, C. and Agudelo C. Species of the genus Bacillus: macroscopic and microscopic morphology. Recovered from: revistabiomedica.org.

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