B. cereus is the cause of about 500 confirmed foodborne illness cases annually in EU countries. B. cereus is known as an opportunistic pathogen and is generally found in soil. B. cereus is a gram-positive, motile rod- and spore-forming bacteria. It is commonly found in the environment and milk in the form of aerobic spore-forming bacteria. B. cereus is a common contaminant of dairy products. B. cereus was renowned as a food-poisoning pathogen in the Bacillus group for 40 years.
Worldwide data of B.cereus outbreaks:
B. cereus outbreaks were the most common and most dangerous type of microbial poisoning in China, accounting for 10.83% of all cases between 2002 and 2017. B. cereus is responsible for 3350 foodborne illness cases in Australia annually. With 247 outbreaks in 2014 that led to 2349 human cases and 18 hospitalizations, B. cereus was the second most common cause of food-borne outbreaks in France.
Detection of B. cereus as a food poisoning agent:
The first time food poisoning due to B. cereus was studied by Led Hauge in 1950, the source of consumption was vanilla sauce. Symptoms were followed by diarrhea, nausea, and abdominal pain. It was truly caused by B. cereus because, after the first attempt, they ingested the self-contaminated sauce with a food-poisoning pathogen strain. The symptoms occurred after 12 hours of consumption of the sauce. Thus, B. cereus was recognized as a causative agent of several food poisoning diseases.
Foods Known for B.cereus Contamination:
Numerous food types have been studied for B. cereus contamination, and market sampling collections of fresh vegetables, dairy goods, starch-rich items, quick-frozen foods, and aquatic products showed high detection rates ranging from 25% to 74%.
Toxins produced by B.cereus:
B. cereus secretes different types of toxins and enzymes that cause diseases, including four types of hemolysin toxins, three different phospholipases, emetic syndrome-causing toxins, and three enterotoxins. Enterotoxins include hemolysin (HBL), cytotoxin K, and non-hemolytic toxin (NHE).
Hemolysin and non-hemolysin toxins are termed enterotoxins due to genetic similarities with bacterial toxins and associated with different foodborne diseases. These toxins are further comprised of different protein subunits and different binding factors.
Diarrheal tripartite enterotoxins comprise two hemolytic subunits and a binding component (B), labeled as HBL. Non-hemolytic enterotoxin is also composed of three subunits and induces emesis in the small intestine, designated as NHE. The emetic syndrome usually occurs due to the intake of contaminated foods, including rice, milk, and pasta. The non-hemolytic enterotoxin has three subunits: nheA, nheB, nheC, and different lytic and binding factors. A single gene encodes for each subunit, and all three genes are present in a single operon. Each subunit has a biological effect, but maximum activity will be observed when all three subunits are present.
Ingestion of B.cereus cereus toxin:
Vegetative cells are consumed as viable cells or spores in the gastrointestinal tract and produce protein-made enterotoxins that cause diarrhea. Emetic toxins are produced as cereulide (a plasmid-encoded cyclic peptide) in different food products and cause emetic syndrome after ingestion of food.
Intestinal illnesses caused by B.cereus:
B. cereus is highly identified as the causative agent of intestinal and non-intestinal diseases. It causes two different diseases related to food poisoning: Emetic syndrome and Diarrheal syndrome
The emetic syndrome is caused by an emetic toxin, also known as cereulid. It is extremely stable (at least two months at 4°C), resistant to proteolytic enzymes, and resistant to temperature (90 min at 126°C). Since it is already present in the food, neither cooking nor digestion will eliminate it. The emetic toxin has a dosage response of 8 mg per kilogram of body weight. A food item is deemed potentially hazardous if it includes 105–106 B. cereus sensu stricto cells.
The diarrheal syndrome: Three enterotoxins—HBL, Nhe, and/or CYTK—that are produced in the colon by a large number of consumed cells or spores are the cause of the diarrheal illness. The enterotoxins are susceptible to proteolysis and acidic environments, and they are heat-labile. When food is cooked or digested in the stomach, it is destroyed. Foods with at least 103–105 cfu-1 are thought to have an excessive number of cells that will not be broken down by digestion but instead colonize the host’s gut and produce enough enterotoxins to induce illness.
Disease-Spectrum of Bacillus cereus (Non-intestinal):
B. cereus causes different diseases other than gastrointestinal infections, including systemic and local infections in immunocompetent and immunocompromised persons. The disease spectrum of B. cereus includes meningitis and brain abscesses, pneumonia, fulminant bacteremia, and cutaneous infections like gas-gangrene.
Prevention of B.cereus Contamination:
Controlling food preparation and storage temperatures is one of the easiest ways to stop B. cereus reproduction. While some cooking techniques (such as steaming, roasting, frying, or grilling) can destroy vegetative cells and spores, low-temperature cooking (below 100 °C) permits spores to survive. One of the primary causes of B. cereus toxication is improper food maintenance, which can be prevented by avoiding permissive temperatures, such as maintaining consistently high temperatures (“hot bond”) or quick cooling.
References
Granum, P. E., & Lindbäck, T. (2012). Bacillus cereus. Food microbiology: Fundamentals and frontiers, 491-502.
Rafique, A., Luqman, M., Nawaz, Z., Ashraf, A., Nasir, S., Asif, A. R., … & Asad, F. (2020). Multiplex PCR based detection of toxin producing Bacillus cereus from different milk samples retailed in Pakistan. Pakistan Journal of Agricultural Sciences, 57(3).
Griffiths, M. W., & Schraft, H. (2017). Bacillus cereus food poisoning. In Foodborne diseases (pp. 395-405). Academic Press.
Berthold-Pluta, A., Pluta, A., Garbowska, M., & Stefańska, I. (2019). Prevalence and toxicity characterization of Bacillus cereus in food products from Poland. Foods, 8(7), 269.
Can, H. Y., Elmalı, M., Karagöz, A., & Dişli, H. B. (2021). Psychrotrophic properties, toxigenic characteristics, and PFGE profiles of Bacillus cereus isolated from different foods and spices. Ciência Rural, 52(4), 20210166.
