Bacillus cereus food poisoning with foodborne toxins

Bacillus cereus is a type of bacteria that can cause food poisoning and other infections in humans. It is widely distributed in nature and can be found in soil, plants, water, dust and the gastrointestinal tract of animals and insects. It can also contaminate various foods and food processing equipment due to its ability to form resistant spores that can survive high temperatures, radiation, desiccation and disinfectants.

Bacillus cereus can produce two types of toxins that are responsible for different forms of food poisoning: diarrheal and emetic. The diarrheal toxin is produced by the bacteria in the small intestine after ingestion of contaminated food, and causes watery diarrhea, abdominal cramps and sometimes bloody stools. The emetic toxin is preformed in the food before consumption, and causes nausea, vomiting and abdominal pain. The symptoms usually appear within a few hours or days after eating the contaminated food and last for 24 to 48 hours.

Bacillus cereus can also cause non-intestinal infections, such as eye infections, respiratory infections and wound infections. These infections are more serious and can lead to complications such as septicemia, pneumonia, meningitis, liver failure and brain edema. They are more likely to occur in people with weakened immune systems or other injuries or wounds caused by surgery or trauma.

Bacillus cereus is one of the most common causes of food poisoning in the world, also known as \"fried rice syndrome\" because it is often associated with cooked rice that has been left at room temperature for too long. Other foods that can be contaminated by Bacillus cereus include dairy products, meat products, pasta, pastry, potatoes, sushi, cheese, soups, stews, vegetables and fruits.

Bacillus cereus food poisoning can be prevented by proper food handling practices, such as cooking food thoroughly, refrigerating leftovers promptly, reheating food before consumption and avoiding cross-contamination. Bacillus cereus food poisoning is usually self-limiting and does not require treatment, except for fluid replacement and bed rest. However, in severe cases or in people with compromised immune systems, antibiotics may be needed.

Bacillus cereus is a bacterium that can cause both mild and serious illnesses in humans. It is important to be aware of its sources, symptoms and prevention measures to avoid getting sick from this organism.

Bacillus cereus is a bacterium that has the following biological characteristics:

• It is a Gram-positive bacterium, meaning that it has a thick layer of peptidoglycan in its cell wall and stains purple with the Gram stain method.
• It is a rod-shaped bacterium, also known as a bacillus.
• It is a spore-former, meaning that it can produce dormant and resistant structures called endospores that can survive in harsh conditions such as high heat, radiation, desiccation and disinfectants .
• It is aerobic-to-facultative, meaning that it can grow in the presence or absence of oxygen.
• It is motile, meaning that it can move by using flagella, which are long and thin appendages that propel the bacterium .
• It can grow on a temperature range of 8 to 55°C, with an optimum temperature of 25 to 37°C.
• It can grow on a pH range of 4.9 to 9.3.
• It can tolerate a salt concentration of up to 7.5%.
• It produces various toxins that can cause food poisoning or other infections in humans and animals .

Bacillus cereus belongs to the Bacillus cereus group, which comprises seven closely related species: B. cereus sensu stricto, B. anthracis, B. thuringiensis, B. mycoides, B. pseudomycoides, B. weihenstephanensis and B. cytotoxicus. These species share many biological characteristics but differ in their pathogenicity and ecology.

Bacillus cereus is widely distributed in nature and can be found in soil, water, plants and animals. It can also contaminate food products such as rice, dairy, meat, vegetables and spices due to its spore-forming nature and ability to form biofilms on surfaces . Bacillus cereus can cause two types of food poisoning: diarrheal and emetic, depending on the type of toxin produced by the bacterium . Bacillus cereus can also cause opportunistic infections such as bacteremia, septicemia, pneumonia, meningitis and endophthalmitis in immunocompromised or injured individuals .

Bacillus cereus is a bacterium of medical importance due to its pathogenic potential and its widespread occurrence in the environment and food products. Therefore, it is important to understand its biological characteristics and how they affect its growth, survival and virulence.

Bacillus cereus is widely distributed in nature and can be found in various environments such as soil, plants, water, dust and the gastrointestinal tracts of insects and mammals . Due to its ability to form resistant endospores, B. cereus can survive in harsh conditions and contaminate a large number of raw materials and food products .

Some of the common sources of contamination by B. cereus are:

• Soil: B. cereus spores can adhere to the surfaces of vegetables and crops that grow in contact with soil. Soil can also contaminate dairy products through feces, bedding, feed and silage on dairy farms.
• Rice: Rice is one of the most frequently implicated foods in B. cereus food poisoning, especially the emetic type. B. cereus spores can survive cooking and germinate during improper cooling or storage of cooked rice .
• Dairy products: Milk and other dairy products can be contaminated by B. cereus spores in raw milk or by post-pasteurization contamination along the processing lines. Cheese, cream, custard and ice cream are also susceptible to B. cereus growth .
• Meat products: Meat products such as poultry, beef, pork and lamb can be contaminated by B. cereus spores during slaughter, processing or storage. Cooked meat dishes such as stews, casseroles and pies can also support B. cereus growth if not properly refrigerated or reheated .
• Other foods: B. cereus can also contaminate other foods such as pasta, pastry, potatoes, sushi, fish, soups, sauces, spices and infant foods . Foods that are high in starch or protein and have a neutral pH are favorable for B. cereus growth.

To prevent B. cereus food poisoning, it is important to avoid or minimize the contamination of foods by these sources and to follow good hygiene and food handling practices.

Bacillus cereus food poisoning is a common but often underreported cause of gastrointestinal illness worldwide. It can occur sporadically or in outbreaks associated with various types of foods, especially cooked rice, meat, vegetables, dairy products and sauces. The incidence of B. cereus food poisoning varies by region and may depend on the food habits, cooking practices and surveillance systems of different countries.

According to the U.S. Food and Drug Administration (FDA), B. cereus accounted for 2% of foodborne outbreaks with confirmed etiology reported to the Centers for Disease Control and Prevention (CDC) during 1973-1987. However, this may be an underestimate as many cases are not diagnosed or reported. In a study of foodborne pathogens in the United States from 1998 to 2008, B. cereus was estimated to cause 63,400 illnesses annually.

In Europe, B. cereus was the fourth most common bacterial agent responsible for foodborne outbreaks in 2018, with 156 outbreaks affecting 2,214 people. The most frequently implicated foods were mixed foods (such as salads, sandwiches and casseroles), rice dishes, meat products and dairy products.

In Asia, B. cereus is a major cause of food poisoning due to the widespread consumption of cooked rice and other starchy foods that are often kept at room temperature for long periods. For example, in Japan, B. cereus was the second most common cause of foodborne outbreaks in 2019, with 1,057 outbreaks affecting 12,751 people. The majority of outbreaks were caused by the emetic toxin and involved rice dishes.

Some examples of B. cereus food poisoning outbreaks reported in the literature are:

• In Norway in 1971, an outbreak of diarrheal illness affected 75 patients in two hospitals after eating contaminated vanilla sauce that was prepared with boiled milk and stored at room temperature for several hours.
• In the United Kingdom in 1974, an outbreak of emetic illness affected over 1,000 people who ate fried rice from a Chinese restaurant that was cooked the day before and reheated inadequately.
• In Hungary from 1960 to 1968, B. cereus was the third most common cause of bacterial food poisoning, with 117 outbreaks involving mainly meat products and dairy products.
• In Taiwan in 1996, an outbreak of diarrheal illness affected 26,173 people with 20 deaths after consuming contaminated soybean sprouts that were grown with contaminated water.
• In Canada in 2003, an outbreak of emetic illness affected 36 people who ate pasta salad that was prepared with cooked pasta that was stored at room temperature for over 24 hours.
• In France in 2005, an outbreak of emetic illness affected 98 people who ate couscous that was contaminated by B. cereus spores during production and stored at room temperature for several days.
• In Australia in 2006, an outbreak of emetic illness affected 73 people who ate fried rice from a Chinese restaurant that was cooked the day before and reheated inadequately.
• In Brazil in 2013, an outbreak of diarrheal illness affected 136 people who ate lasagna that was prepared with contaminated cheese and stored at room temperature for several hours.

Bacillus cereus food poisoning can be prevented by proper handling, cooking and storage of foods, especially those that are rich in starch or protein and have a neutral pH. Foods should be cooked thoroughly to kill vegetative cells and spores, cooled rapidly to prevent spore germination and toxin production, and refrigerated at below 4°C or heated above 60°C until consumption. Foods that are left at room temperature for more than two hours should be discarded.

Bacillus cereus produces two types of protein toxins that can cause food poisoning: diarrheal toxin and emetic toxin .

Diarrheal toxin

• The diarrheal toxin is formed when vegetative cells of B. cereus grow in the small intestine after ingestion of contaminated food .
• The diarrheal toxin is sensitive to proteases such as pronase, pepsin, trypsin and chymotrypsin .
• The infectious dose of B. cereus that can cause diarrheal illness is about 10⁴ to 10⁹ cfu/g of food .
• The incubation period of diarrheal illness ranges from 8 to 16 hours and the symptoms last for 12 to 24 hours .
• The symptoms of diarrheal illness include watery diarrhea, abdominal pain and cramps . In some cases, bloody diarrhea and necrotic enteritis may occur, leading to liver failure and brain edema.
• There are three chromosomally encoded enterotoxins associated with diarrheal illness: hemolysin BL (Hbl), nonhemolytic enterotoxin (Nhe) and cytotoxin K (CytK) .
• Hbl is a three-component toxin that forms a transmembrane pore in the small intestine by osmotic lysis . It is a primary virulence factor in B. cereus diarrheal food poisoning.
• Nhe is a three-component toxin that has similar homology to Hbl and also forms a pore-forming toxin .
• CytK is a single-component toxin that resembles a prototype toxin that causes bloody diarrhea and necrotic enteritis . It is a β-barrel pore-forming toxin.

Emetic toxin

• The emetic toxin is a small cyclic heat-stable peptide that is produced by B. cereus in the food before ingestion .
• The emetic toxin is resistant to heat, acid, proteases and radiation .
• The infectious dose of B. cereus that can cause emetic illness is about 10⁵ to 10⁸ cfu/g of food .
• The incubation period of emetic illness ranges from 1 to 5 hours and the symptoms last for up to 24 hours .
• The symptoms of emetic illness include nausea, vomiting and abdominal cramps . It resembles staphylococcal food poisoning.
• The mode of action of the emetic toxin is not fully understood, but it is believed that it forms ion channels and holes in the membrane .
• The emetic toxin is also known as cereulide and can be detected by liquid chromatography-mass spectrometry (LC-MS) methods.

The diarrheal toxin is a type of enterotoxin that is produced by some strains of Bacillus cereus in the small intestine after ingestion of contaminated food. It causes watery diarrhea, abdominal cramps and sometimes fever within 8 to 16 hours of exposure. The illness is usually self-limiting and lasts for 24 to 48 hours.

The diarrheal toxin is sensitive to proteases such as pronase, pepsin, trypsin and chymotrypsin. It is estimated that the infectious dose of Bacillus cereus for causing diarrheal illness is about 10^4 to 10^9 colony forming units (cfu) per gram of food.

There are three types of diarrheal toxins that have been identified in Bacillus cereus: hemolysin BL (Hbl), nonhemolytic enterotoxin (Nhe) and cytotoxin K (CytK) .

• Hbl is a three-component toxin that forms pores in the plasma membrane of intestinal epithelial cells, leading to osmotic lysis and cell death. Hbl is considered the primary virulence factor in Bacillus cereus diarrheal food poisoning .
• Nhe is another three-component toxin that has a similar structure and mode of action to Hbl, but with a lower hemolytic activity. Nhe also forms pores in the plasma membrane of intestinal epithelial cells and causes cytotoxicity .
• CytK is a single-component toxin that belongs to the beta-barrel pore-forming toxin family. CytK can cause necrotic enteritis, a severe form of diarrheal illness that is characterized by bloody diarrhea, tissue damage and systemic complications. CytK can also induce apoptosis and inflammation in intestinal epithelial cells .

The three types of diarrheal toxins can act synergistically to enhance their cytotoxic effects on intestinal epithelial cells. The expression and secretion of these toxins are regulated by various environmental factors such as temperature, pH, oxygen, carbon dioxide, nutrients and quorum sensing .

The emetic toxin is a small cyclic peptide that is produced by some strains of B. cereus in food before ingestion. It is also known as cereulide and has a molecular mass of 1.2 kDa. It consists of three repeats of four amino and/or oxy acids: 3 . This structure is similar to the potassium ionophore valinomycin, which can form pores in cell membranes and disrupt the ion balance.

The emetic toxin is heat-stable and can survive cooking procedures such as boiling, frying, roasting and microwaving . It is also resistant to acid, proteases and other enzymes. The toxin can be detected by various methods such as liquid chromatography-mass spectrometry (LC-MS), enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR).

The emetic toxin causes nausea, vomiting and abdominal cramps within one to six hours after ingestion of contaminated food. The symptoms are similar to those of staphylococcal food poisoning and usually last for less than 24 hours . The dose of toxin required to cause illness is estimated to be 0.1 to 0.2 μg per kg of body weight. The mode of action of the toxin is not fully understood, but it may involve binding to serotonin receptors in the brain and stimulating the vomiting center.

The most common food associated with the emetic toxin is cooked rice, especially fried rice from Chinese restaurants. This is because rice provides a suitable environment for B. cereus growth and toxin production after cooking and cooling . Other foods that have been implicated in emetic outbreaks include pasta, pastry, potatoes, cheese, sushi and other starchy foods .

Bacillus cereus is a foodborne pathogen that can cause two types of food poisoning: diarrheal and emetic. The detection of B. cereus and its toxins in food samples is important for food safety and public health. There are various methods available for the detection of B. cereus and its toxins, ranging from conventional culture methods to advanced molecular and biosensor methods. Here are some of the commonly used methods:

• Culture methods: These methods involve the isolation and enumeration of B. cereus from food samples using selective and differential media, such as mannitol-egg yolk-polymyxin B agar (MYP) or polymyxin B-pyruvate-egg yolk-mannitol-bromothymol blue agar (PEMBA). These media allow the growth of B. cereus and inhibit the growth of other bacteria. Typical colonies of B. cereus appear as pink or orange with a zone of precipitation around them. The culture methods are simple, inexpensive and reliable, but they are time-consuming (24 to 48 hours) and may not differentiate between B. cereus and other closely related species.

• ELISA: ELISA (enzyme-linked immunosorbent assay) is a technique that uses antibodies to detect specific antigens, such as toxins or cell surface proteins, in a sample. ELISA can be used to measure the amount of diarrheal or emetic toxins produced by B. cereus in food samples. However, ELISA has some limitations, such as low specificity, cross-reactivity and interference by other substances.

• PCR: PCR (polymerase chain reaction) is a technique that amplifies a specific DNA sequence in a sample using primers and enzymes. PCR can be used to detect the presence of toxin genes or other virulence factors in B. cereus isolates or food samples. PCR is highly sensitive, specific and rapid, but it requires specialized equipment and trained personnel.

• Biosensors: Biosensors are devices that combine a biological recognition element (such as an antibody, a phage or a cell) with a physical transducer (such as an optical, electrical or mechanical signal) to generate a measurable response upon binding to a target analyte (such as a toxin or a bacterium). Biosensors can be used to detect B. cereus and its toxins in food samples with high sensitivity, specificity and speed. Biosensors can also be portable, user-friendly and low-cost. Some examples of biosensors for B. cereus detection are:

  • Phage-based biosensors: These biosensors use bacteriophages (viruses that infect bacteria) that are specific for B. cereus as the biological recognition element. The phages bind to the surface of B. cereus cells and trigger a signal that can be detected by an optical or electrical transducer.
  • Cell-based biosensors: These biosensors use living cells (such as mammalian cells or bacterial cells) that are genetically modified to express receptors or reporters for B. cereus toxins as the biological recognition element. The cells respond to the toxins by changing their morphology, metabolism or fluorescence, which can be detected by an optical or electrical transducer.
  • Immunosensors: These biosensors use antibodies that are specific for B. cereus toxins as the biological recognition element. The antibodies bind to the toxins and generate a signal that can be detected by an optical or electrical transducer.
  • DNA biosensors: These biosensors use DNA probes that are complementary to the toxin genes or other virulence factors of B. cereus as the biological recognition element. The DNA probes hybridize with the target DNA sequences and generate a signal that can be detected by an optical or electrical transducer.

These are some of the advanced methods for detection of Bacillus cereus and its pathogenic factors in food samples. Each method has its own advantages and disadvantages, depending on the type of sample, the level of contamination, the availability of resources and the desired accuracy. Therefore, it is important to choose the most suitable method for each case.

Bacillus cereus food poisoning is usually a self-limiting illness that resolves within 24 to 48 hours . The main treatment is to rest and drink plenty of fluids to prevent dehydration from vomiting and diarrhea . Fluids that contain electrolytes, such as sodium and minerals, can help replenish the salts lost by the body.

In some cases, especially for people with severe dehydration or a weak immune system, intravenous fluid and electrolyte replacement may be necessary. This involves getting fluids through a needle inserted into a vein.

Antibiotics are not indicated for Bacillus cereus food poisoning, as they do not affect the toxins produced by the bacteria. Antibiotics may also cause adverse effects or increase the risk of antibiotic resistance.

Most people with Bacillus cereus food poisoning recover without complications. However, some people may develop more serious infections or conditions, such as bacteremia, septicemia, pneumonia, meningitis, gastritis, liver failure, liver necrosis and brain edema. These cases require prompt medical attention and appropriate treatment.

Bacillus cereus food poisoning can be prevented by following good hygiene and food safety practices. Some of the measures that can help reduce the risk of B. cereus contamination and illness are:

• Wash your hands with soap and water before and after handling food, especially raw meat, poultry, fish, eggs and dairy products.
• Wash fruits and vegetables thoroughly under running water, especially if they have been in contact with soil, dust or animal feces.
• Cook food thoroughly and use a food thermometer to check the internal temperature of meat, poultry and seafood. The recommended temperatures are 165°F (74°C) for poultry, 160°F (71°C) for ground meat and 145°F (63°C) for whole cuts of meat and fish.
• Keep hot foods hot (above 140°F or 60°C) and cold foods cold (below 40°F or 4°C) to prevent the growth of B. cereus and other bacteria .
• Refrigerate or freeze leftovers within two hours of cooking or serving. Do not leave cooked rice or other starchy foods at room temperature for more than two hours.
• Reheat leftovers thoroughly before eating and discard any food that looks or smells spoiled or has been stored for too long.
• Avoid cross-contamination by using separate cutting boards, utensils and containers for raw and cooked foods. Wash and sanitize them after each use.
• Follow the label instructions on packaged foods and check the expiration dates before buying or consuming them.
• Educate yourself and others about the symptoms and causes of B. cereus food poisoning and seek medical attention if you suspect you have been infected.

By following these prevention and control measures, you can protect yourself and others from B. cereus food poisoning and enjoy your food safely.

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