What is Bacillus cereus?

Bacillus cereus is a pathogenic bacterium known for causing food-borne illnesses. Here is information about Bacillus cereus:

1. Widely Distributed: Bacillus cereus is widely distributed in nature. It can be found in various environments, including plants, soils, and the gastrointestinal tracts of insects and mammals.
2. Contamination of Food: Bacillus cereus is capable of contaminating raw materials and food products, particularly due to the presence of resistant endospores. These endospores can survive harsh conditions, including heat, allowing them to persist and potentially cause illness when consumed.
3. Two Types of Food Poisoning: Bacillus cereus is responsible for two types of food poisoning diseases. The first type is the diarrheal type, caused by the production of a complex enterotoxin in the small intestine. The second type is the emetic type, which results from the consumption of food containing heat-stable toxins.
4. Diarrheal Type: The diarrheal type of Bacillus cereus food poisoning is characterized by symptoms such as abdominal pain, watery diarrhea, and nausea. The onset of symptoms typically occurs within 8-16 hours after consuming contaminated food.
5. Emetic Type: The emetic type of Bacillus cereus food poisoning is associated with symptoms such as vomiting and nausea. The symptoms usually appear within 1-5 hours after ingesting food containing heat-stable toxins.
6. Opportunistic Infections: Bacillus cereus can also cause opportunistic infections, particularly in individuals with weakened immune systems. These infections can include bacteremia, septicemia, pneumonia, meningitis, gastritis, liver failure, liver necrosis, and brain edema.
7. Other Bacillus Species: Apart from Bacillus cereus, other species within the Bacillus genus, such as B. subtilis, B. licheniformis, B. pumilus, B. weihenstephanensis, B. anthracis, B. mycoides, B. pseudomycoides, and B. thuringiensis, are also capable of causing food-borne illnesses.

Biological characteristics of Bacillus cereus

Bacillus cereus possesses specific biological characteristics that contribute to its survival and potential to cause illness. Here are the key characteristics of Bacillus cereus:

1. Gram-Positive Bacteria: Bacillus cereus belongs to the group of gram-positive bacteria, which means its cell wall retains the crystal violet stain during the Gram staining procedure.
2. Spore-Former: Bacillus cereus is known for its ability to form endospores. These endospores are dormant, tough structures that allow the bacterium to withstand harsh environmental conditions and survive unfavorable situations.
3. Aerobic-to-Facultative: Bacillus cereus is capable of thriving in both aerobic (oxygen-rich) and facultative (oxygen-tolerant) environments, adapting to varying oxygen availability.
4. Motile: Bacillus cereus is motile, meaning it has the ability to move using flagella (whip-like appendages) present on its cell surface.
5. Rod-Shaped Bacilli: Bacillus cereus cells have a rod-like shape, commonly referred to as bacilli.
6. Temperature Range: Bacillus cereus can grow over a wide temperature range, from as low as 8°C to as high as 55°C. However, the optimum temperature for growth typically falls within the range of 25 to 37°C.
7. pH Tolerance: Bacillus cereus exhibits a wide pH tolerance range, being capable of growth in environments with a pH range of 4.9 to 9.3.
8. Salt Tolerance: Bacillus cereus can tolerate salt concentrations of up to 7.5%. This ability allows it to survive and potentially grow in foods with moderate salt content.
9. Endospore Resistance: The endospores produced by Bacillus cereus are highly resistant to adverse conditions, including high heat, radiation, desiccation (drying), and disinfectants. This resistance contributes to the survival and persistence of the bacterium in the environment and in food-related settings.

Sources of contamination

Bacillus cereus can contaminate various sources, leading to potential foodborne outbreaks. Here is information about the sources of contamination associated with Bacillus cereus:

1. Food Processing Units: The heat-resistant spores of Bacillus cereus can contaminate the entire food processing chain, from raw materials to packaging and storage. Contamination can occur during various stages of food processing and handling.
2. Biotechnological Equipment: Equipment and machinery used in biotechnological processes can also become contaminated with Bacillus cereus. Improper cleaning and sanitation practices may contribute to the persistence and spread of the bacterium.
3. Soil: Bacillus cereus is naturally found in soil, and this is a significant source of contamination. The bacterium can easily be transmitted from soil to vegetables and crops during cultivation and harvesting.
4. Food Products: Bacillus cereus contamination is commonly found in a range of food products. Examples include rice, wheat, pasta, flour, dairy products, meat products, spices, infant foods, fish, soups, vegetables, and fruits. These foods can become contaminated at various stages, including during production, processing, and storage.
5. B. thuringiensis Biopesticide: Bacillus thuringiensis (Bt), a close relative of Bacillus cereus, is commonly used as a biopesticide to control pests in agriculture. However, when Bt is spread on plants and vegetation, it can produce enterotoxins, affecting the health of consumers if ingested.
6. Reported Outbreaks: Bacillus cereus contamination has been associated with numerous foodborne outbreaks. Consumption of contaminated food has led to cases of food poisoning and illness in various populations.

Epidemiology and outbreaks of Bacillus cereus Food Poisoning

The epidemiology and outbreaks of Bacillus cereus food poisoning have been observed in various regions. Here is information about the epidemiology and outbreaks associated with Bacillus cereus:

1. Initial Outbreak in Norwegian Hospitals: The first reported outbreak of Bacillus cereus food poisoning occurred in Norwegian hospitals. However, no specific populations affected by the outbreak were described. The affected individuals experienced watery diarrhea, particularly among the elderly and those with low stomach acid.
2. UK Outbreak from Contaminated Rice: In 1971, a significant outbreak occurred in the United Kingdom when individuals consumed contaminated rice from a Chinese restaurant. The outbreak resulted in approximately 1,000 cases of nausea and vomiting.
3. High Incidence in Hungary: Bacillus cereus food poisoning is the third most common bacterial outbreak in Hungary, with 117 reported outbreaks between 1960 and 1968. This highlights the significant impact of Bacillus cereus contamination on the population in this region.
4. Outbreaks in Japan: Between 1982 and 1986, Japan experienced 73 reported outbreaks of Bacillus cereus food poisoning, affecting a total of 1,323 individuals. These outbreaks signify the prevalence of Bacillus cereus contamination in the country.
5. Taiwan Outbreaks: Taiwan has also seen a substantial number of cases related to Bacillus cereus food poisoning. An outbreak in Taiwan resulted in 26,173 reported cases, including 20 deaths. Bacillus cereus accounted for 18% of the cases.
6. Global Distribution: Bacillus cereus food poisoning is reported every year in various geographically distributed nations, including Scotland, Japan, the UK, Iceland, England and Wales, Northern Europe, and North America. The bacterium has the potential to cause outbreaks in different regions.
7. Varied Outbreak Frequency: The number of reported outbreaks of Bacillus cereus food poisoning varies between countries. England and Wales, Japan, the USA, and Canada have reported a lower number of outbreaks compared to other countries. This discrepancy may be attributed to differences in cooking and eating habits, as well as variations in surveillance and reporting systems.

Monitoring and prevention efforts, along with proper food handling and hygiene practices, are necessary to minimize the occurrence and impact of Bacillus cereus food poisoning outbreaks worldwide.

Bacillus cereus foodborne toxins

Bacillus cereus produces protein toxin, including diarrheal toxin as well as emetictoxin.

Diarrheal toxin

The diarrheal toxin produced by Bacillus cereus plays a significant role in causing diarrheal food poisoning. Here is information about the diarrheal toxin:

1. Formation in the Small Intestine: When vegetative cells of Bacillus cereus are consumed in contaminated food, they can grow and produce diarrheal toxins in the small intestine.
2. Sensitivity to Proteases: Diarrheal toxins produced by Bacillus cereus are sensitive to proteases, such as pronase, pepsin, trypsin, and chymotrypsin. This sensitivity affects the activity and stability of the toxins.
3. Infectious Dose: The total infectious dose required to cause diarrheal illness is estimated to be between 104 and 109 colony-forming units (cfu) per gram of contaminated food.
4. Incubation Period: The incubation period for Bacillus cereus diarrheal food poisoning typically ranges from 8 to 16 hours after ingestion. Symptoms usually emerge within this timeframe and last for 24 to 48 hours.
5. Mild Symptoms: The symptoms associated with Bacillus cereus diarrheal food poisoning are generally mild and include watery diarrhea and abdominal cramps.
6. Severe Symptoms: In some cases, particularly among children and immunocompromised individuals, more severe symptoms may occur. These can include bloody diarrhea, necrotic enteritis (intestinal tissue death), and complications such as liver failure and brain edema.
7. Enterotoxins: Bacillus cereus produces three chromosomally encoded enterotoxins associated with diarrheal illness. These include Hemolysin BL (Hbl), Nonhemolytic enterotoxin (Nhe), and Cytotoxin K (CytK).
8. Hemolysin BL (Hbl): Hbl is considered a primary virulence factor in Bacillus cereus diarrheal food poisoning. It forms a transmembrane pore in the small intestine through osmotic lysis.
9. Nonhemolytic enterotoxin (Nhe): Nhe shares homology with Hemolysin BL and is also a three-part component toxin involved in the pathogenesis of Bacillus cereus diarrheal illness. It also functions as a pore-forming toxin.
10. Cytotoxin K (CytK): CytK is a toxin that shares similarities with a prototype toxin known for causing bloody diarrhea and necrotic enteritis. It acts as a β-barrel pore-forming toxin.

Emetic toxin

The emetic toxin produced by Bacillus cereus is responsible for causing the emetic type of food poisoning. Here is information about the emetic toxin:

1. Severity and Acuteness: The emetic response induced by Bacillus cereus is characterized by a more severe and acute reaction. This is attributed to a small cyclic heat-stable peptide, which acts as the emetic toxin.
2. Incubation Period: The incubation period for Bacillus cereus emetic food poisoning typically ranges from 2 to 5 hours after ingestion of preformed toxin-contaminated foods. Symptoms manifest relatively quickly after consuming the contaminated food.
3. Infectious Dose: A higher bacterial load of approximately 105 to 108 cells per gram of food is required to cause the emetic illness.
4. Symptoms: The symptoms of Bacillus cereus emetic food poisoning resemble those of Staphylococcus aureus food poisoning. They include nausea, vomiting, and abdominal cramps, which typically last for about 24 hours.
5. Mode of Action: The exact mode of action of the emetic toxin is still not fully understood. However, it is believed that the cereulide toxin, with a molecular weight of 1.2 kDa, forms ion channels and pores in the cell membrane, leading to the emetic response.
6. Heat Stability: The emetic toxin produced by Bacillus cereus is heat stable, meaning it can withstand cooking procedures such as frying, roasting, boiling, and microwaving. This resilience allows the toxin to persist in cooked food.
7. Environmental Factors: Several environmental factors influence the toxicity of Bacillus cereus. These factors include temperature, pH, atmospheric composition, nutrient sources, and food consistency. Optimal conditions for toxin production and activity may vary depending on these factors.

Detection methods of Bacillus cereus

Detection methods for Bacillus cereus involve various techniques to identify the presence of the bacterium and its toxins. Here is information about different detection methods for Bacillus cereus:

1. Culture Methods: Laboratory culture methods involve using nutrient agar or blood agar for Bacillus cereus culture. Selective media like polymyxin B-pyruvate-egg yolk-mannitol-bromothymol blue agar (PEMBA) and mannitol-egg yolk-polymyxin B agar (MYP) are used for polymyxin B resistant strains. After 24 hours of incubation, pink colonies with a clear zone of precipitation may be observed. The most probable number (MPN) technique is used when the organism is present in low numbers. Presumptive, confirmatory, and completed tests are conducted to confirm the presence of Bacillus cereus.
2. ELISA: Enzyme-linked immunosorbent assay (ELISA) is a commercially available technique used to measure the toxins produced by Bacillus cereus. However, it may not accurately assess the toxin-producing activity. ELISA can detect either the hemolysin BL toxin or two nontoxic proteins.
3. Reverse Passive Latex Agglutination (RPLA) Enterotoxin Assay: In this test, the sample is boiled to inactivate the biological activity of the toxins. The test primarily recognizes the hemolysin B component. However, in the presence of a high glucose concentration, the toxins may become undetectable.
4. PCR: Polymerase chain reaction (PCR) assays can be used to detect the presence of Bacillus cereus DNA sequences, including toxin genes. PCR assays provide information about the presence of virulent strains and their toxin production. Complementary tests may be required to confirm the presence of specific toxin genes.

Treatment of Bacillus cereus Food Poisoning

The treatment of Bacillus cereus food poisoning typically involves supportive care, as the illness is self-limiting and resolves within 24 to 48 hours. Here is information about the treatment options:

1. Bed Rest: Bed rest is recommended for individuals with Bacillus cereus food poisoning. Resting allows the body to recover and heal more efficiently.
2. Fluid Therapy: Fluid therapy is an essential aspect of treatment for Bacillus cereus food poisoning. It helps to prevent dehydration caused by symptoms like diarrhea and vomiting. Rehydration can be achieved through oral rehydration solutions or, in severe cases, intravenous fluids may be necessary.
3. Antibiotics (in severe cases): In severe cases or when complications arise, antibiotic treatment may be considered. Antibiotics such as clindamycin, vancomycin, gentamicin, and chloramphenicol may be prescribed. However, it’s important to note that antibiotics are generally not necessary for most cases of Bacillus cereus food poisoning and are typically reserved for severe or systemic infections.

Prevention and control measures of Bacillus cereus Food Poisoning

Prevention and control measures are crucial in reducing the risk of Bacillus cereus food poisoning. Here is information about these measures:

1. Eliminate Contamination: It is important to eliminate contamination of food products by Bacillus cereus before the germination of spores. This can be achieved through proper cleaning and sanitation practices in food processing areas, equipment, and utensils.
2. Rapid Cooling and Reheating: Rapidly cooling cooked food before storage and ensuring proper reheating before consumption can help prevent the growth and toxin production of Bacillus cereus. Proper temperature control is important to inhibit bacterial growth.
3. Low pH Foods: Bacillus spp. are not able to survive in foods with low acidity (pH 4.3 or below). Consuming foods with low pH, such as acidic fruits and vegetables, can help reduce the risk of Bacillus cereus food poisoning.
4. Traceability and Control: In food processing plants, trace the presence of Bacillus cereus spores from farm to packaging. Implementing quality control measures and monitoring the production process can help identify potential sources of contamination and prevent the spread of Bacillus cereus.
5. Food Handling Practices and Hygiene: Proper food handling practices, including regular handwashing, using clean utensils, and avoiding cross-contamination between raw and cooked foods, are essential to prevent Bacillus cereus contamination. Good personal hygiene among food handlers is crucial in maintaining food safety.
6. Education and Awareness: Educate food handlers on food safety management practices to ensure they are knowledgeable about preventing Bacillus cereus contamination. It is also important to raise awareness among farmers about Bacillus cereus and its potential risks to eliminate food poisoning at the source.

FAQ

References

1. Tewari, A., & Abdullah, S. (2014). Bacillus cereus food poisoning: international and Indian perspective. Journal of Food Science and Technology, 52(5), 2500–2511.
2. Marrollo, R. (2016). Bacillus cereus Food-Borne Disease. The Diverse Faces of Bacillus Cereus, 61–72. 
3. Drobniewski, F. A. (1993). Bacillus cereus and related species. Clinical Microbiology Reviews, 6(4), 324–338.
4. Granum, P. E., & Lund, T. (2006). Bacillus cereus and its food poisoning toxins. FEMS Microbiology Letters, 157(2), 223–228.
5. Parihar, H. S. (2014). Bacillus cereus. Encyclopedia of Toxicology, 353–354.
6. Batt, C. A. (2014). BACILLUS | Bacillus cereus. Encyclopedia of Food Microbiology, 124–128.