Bacillus cereus
Bacillus cereus | ||||||||||||
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Bacillus cereus (flagella stain) |
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Scientific name | ||||||||||||
Bacillus cereus | ||||||||||||
Frankland & Frankland 1887 |
Bacillus cereus is a motile, gram-positive , rod-shaped, catalase- positive , spore-forming , facultatively anaerobic bacterium of the genus Bacillus .
It occurs naturally in normal soil in a concentration of up to one million per gram and is therefore one of the most common cultivable soil bacteria . Together with other species (e.g. Bacillus anthracis , Bacillus thuringiensis and Bacillus cytotoxicus ) it forms the Bacillus cereus group, whose members are genetically closely related and share a core genome of around 3,100 genes . Historically, the diseases that are triggered by them serve as a distinguishing feature. The set of 400 to 800 individual genes ( accessory genome , in Bacillus cereus around 420 genes) of the respective species serves as a genetic distinguishing feature .
properties
Depending on the strain, Bacillus cereus grows in the temperature range from 4 ° C to 55 ° C (most in the range from 10 ° C to 50 ° C), with an optimum of 28–35 ° C.
Bacillus cereus is sensitive to acids. pH range: minimum 4.8; Optimum 6.5-7.5; Maximum 9.3.
The spores are not sensitive to heat, and pasteurization does not kill them.
80% of all fatty acid chains in the bacterium are branched.
Importance to humans
Bacillus cereus is a food-poisoning bacterium that occurs particularly in rice. Bacillus cereus spores, which occur in raw rice, survive cooking and multiply if the rice is kept warm or warmed up below 65 ° C. Keeping them warm above this temperature prevents the bacteria from spreading, which rice cookers make use of with their warming function. However, it can also get into food (spices, dried mushrooms, milk) via dust and soil particles.
Bacillus cereus forms two toxins responsible for food poisoning with bacterial counts of over 100,000 / g of food , although cases of poisoning are also known in which the concentration was well below 6,000 / g. The Federal Institute for Risk Assessment (BfR) recommends that the food surveillance authorities issue a rapid warning in the RASFF at over 10 5 CFU / g during the shelf life . The German Society for Hygiene and Microbiology (DGHM) provides guide and warning values for selected risk foods in cooperation with Beuth Verlag . The lobby organization Federation for Food Law and Food Science (BLL) criticizes the auxiliary standard , since the biological pesticide Bacillus thuringiensis is included in the guideline and warning values for mixed salads, and argues that this creates a distortion of competition . The EFSA recommends the use of whole genome sequencing for the final risk assessment .
A distinction is made between two different types of toxin.
- Vomiting toxin (emetic toxin, cereulide ): Ingestion of the toxin-containing food leads to nausea and vomiting after 0.5 to 6 hours, less often to abdominal cramps and diarrhea. The toxin is insensitive to heat and acid.
- Diarrhea toxin causes watery diarrhea 8 to 16 hours after ingestion of the toxin, which subsides after 12 to 24 hours. The toxin is sensitive to heat and acids.
Bacillus cereus leads to bitterness and sweet coagulation in pasteurized , non- fermented milk products (coagulation by protein-degrading enzymes and not by acid formation). Because of the taste changes caused in this case by this germ by means of the lecithinase effect, the risk of intoxication is not very great.
Since Bacillus cereus in dairy products grows at a temperature in the refrigerator from 10 ° C (some strains from 4 ° C), the declaration of the shelf life for fresh milk was changed from "best at +10 ° C to:" through "at +8 ° C Best before: "changed. The EFSA requires temperatures of ≤ 7 ° C (better still ≤ 4 ° C) to be maintained throughout the cold chain.
Novel forms of anthrax
B. cereus was identified as the causative agent of anthrax-like diseases in humans as early as 2004 .
In 2016, the B. cereus biovar anthracis variety was identified by the Robert Koch Institute as the cause of novel anthrax diseases and deaths in Africa. Until then, various mammal species were affected, in addition to elephants and goats , great apes ( chimpanzees and gorillas ) are particularly affected.
In 2017 it was found that this variety of B. cereus has two additional plasmids ( DNA rings) compared to the usual form . The two plasmids contain all the essential genes that make B. anthracis , the classic anthrax pathogen, a deadly danger. In the meantime, diseases were also found in forest antelopes and porcupines . So far, no diseases have been registered in humans and it is not known whether humans can also develop this form of anthrax. It is feared, however, that the pathogen could decimate or even wipe out local populations of the western chimpanzee ( Pan troglodytes verus , a subspecies of the common chimpanzee ).
The new anthrax variant has been given the name rainforest anthrax.
Diagnosis
Only a determination of so-called presumptive Bacillus cereus is possible using cultural methods . The Bacillus cereus group can be confirmed using MALDI-TOF MS . Only Bacillus cytotoxicus can be reliably differentiated if a suitable database entry is submitted. The NHE and HBL toxins are immune and can be detected using GLISA. A PCR of the nhe / hbl genes is also possible. A ces gene PCR can be used for cereulide-producing B. cereus . The heat-stable and possibly still present emetic toxin cereulide after disinfection can be detected in the food using LC / MS . Biomarkers of cereulide-forming Bacillus cereus can also be detected using MALDI-TOF MS.
Individual evidence
- ↑ Spektrum der Wissenschaft, 4/2008, pp. 14-16, Huge gene reservoir of a pathogen.
- ↑ Bacillus cereus. In: bund.de. www.bfr.bund.de, accessed on February 15, 2017 .
- ↑ a b c d EFSA : Public health risks posed by the Bacillus cereus group , July 20, 2016
- ↑ T. Kaneda: Iso- and anteiso-fatty acids in bacteria: biosynthesis, function, and taxonomic significance. In: Microbiol. Rev. 55 (2); June 1991: pp. 288-302 PMID 1886522 (free full text access ).
- ↑ BfR catalog of criteria for reports in accordance with the General Administrative Regulation : Rapid Alert System for Food and Feed (AVV SWS) Information No. 043/2008 of the BfR of November 20, 2008
- ↑ a b Burkhard Schütze: Bacillus cereus in sight: Bacillus cereus in food - a differentiated risk assessment is possible nowadays! Deutsche Lebensmittel-Rundschau , May 2017, full text on Researchgate
- ↑ Sieglinde Stähle: Statement by DGHM guideline and warning values for “mixed salads” , Association for Food Law and Food Science , Berlin, January 2015
- ↑ Microbiological and Sensory Quality of Milk on the Domestic Market . In: Polish Journal of Food and Nutrition Sciences . tape 65 , no. 4 , December 1, 2015, doi : 10.1515 / pjfns-2015-0008 .
- ^ AR Hoffmaster, J. Ravel et al. a .: Identification of anthrax toxin genes in a Bacillus cereus associated with an illness resembling inhalation anthrax. In: Proceedings of the National Academy of Sciences. 101, 2004, p. 8449, doi : 10.1073 / pnas.0402414101 .
- ↑ Kym S. Antonation, Kim Grützmacher u. a .: Bacillus cereus Biovar Anthracis Causing Anthrax in Sub-Saharan Africa — Chromosomal Monophyly and Broad Geographic Distribution. In: PLOS Neglected Tropical Diseases. 10, 2016, p. E0004923, doi : 10.1371 / journal.pntd.0004923 .
- ^ S. Gerhard: New anthrax pathogen infects animals in Africa , in: Zeit online from September 8, 2016
- ↑ Waldantilopen , in: Academic Universal-Lexikon 2012, accessed on August 5, 2017.
- ↑ a b Constanze Hoffmann, Fee Zimmermann a. a .: Persistent anthrax as a major driver of wildlife mortality in a tropical rainforest. In: Nature. 548, 2017, pp. 82–86, doi : 10.1038 / nature23309 .
- ↑ K. Kupferschmidt: New anthrax pathogen kills great apes, in: Süddeutsche Zeitung (SZ.de) of August 3, 2017.
- ↑ Sebastian Ulrich, Christoph Gottschalk, Richard Dietrich, Erwin Märtlbauer, Manfred Gareis: Identification of cereulide producing Bacillus cereus by MALDI-TOF MS . In: Food Microbiology . tape 82 , p. 75–81 , doi : 10.1016 / j.fm.2019.01.012 ( raps-stiftung.de [PDF]).
Web links
- Bacillus cereus - LAVES
- Bacillus cereus - BfR
- Literature on Bacillus cereus in the catalog of the German National Library