What Is Bacillus Cereus?
Bacillus cereus is an aerobic gram-positive and rod-shaped bacteria capable of forming spores. It can also at times grow in anaerobic conditions, i.e., in the absence of oxygen. This bacterium produces toxins that bring about diarrheal and emetic types of food poisoning.
What Toxins Are Produced by Bacillus Cereus?
The toxins produced are of two types:
The emetic toxin has a ring shape and has a chemical structure similar to that of potassium ionophore valinomycin. It causes emetic types of food poisoning.
The three enterotoxins include the following:
Hemolysin is one of the three enterotoxins. Of the three enterotoxins, two are responsible for food poisoning, while the other toxin is only a simple protein component and shows no involvement. Diarrheal type of food poisoning is associated with enterotoxins.
What Causes Bacillus Cereus Infection?
Bacillus cereus is widely prevalent in the soil. Bacillus Cereus is a soil saprophyte and hence is detected in plants. However, few species have been isolated dairy products, eggs, and meat products.
These bacteria grow on food when placed at room temperature or a favorable temperature, say between 8°C to 55°C for more than 2 hours and at a pH greater than 4.8. Once they grow on the food materials, even heat treatment cannot destroy them. This type of bacteria can even grow on foods that have undergone heat treatment. Spores are responsible for food poisoning, germination of which is enhanced by heat treatment.
The formation of vegetative spores is needed for causing the infection. When the food is contaminated with bacteria producing celeuride toxin, emetic symptoms occur, and diarrheal symptoms occur in those infected with bacteria producing enterotoxins.
For an infection to occur and exhibit symptoms, both diarrheal and emetic, the Bacillus cereus should be present in numbers greater than 10,000 for every gram of food. However, few studies suggest that even fewer numbers can cause infections associated with hospitalization.
What Is Bacillus Cereus Infection?
It is a food-borne bacterial infection characterized by gastrointestinal illnesses like emetic and diarrheal syndromes.
Once contaminated with the Bacillus cereus, symptoms of an emetic syndrome are seen when there is a production of an emetic toxin called cereulide, and diarrheal symptoms are produced with enterotoxin production. Bacteria enter the human body through contaminated food.
How Is Bacillus Cereus Infection Manifested?
Bacillus cereus infection has two types of manifestations, namely:
1. Gastrointestinal Symptoms:
The following are the symptoms associated with emetic-type:
The emetic toxin, cereulide, causes these manifestations, and it can occur within half an hour to six hours of taking foods that have been kept at room temperature, although these foods have been reheated.
Symptoms of diarrheal-type include the following:
Abdominal pain and cramps.
Profuse and watery diarrhea. There can be a discharge of blood or mucus with diarrhea at times.
Sometimes, nausea and vomiting may be associated.
The enterotoxins produced by Bacillus cereus bacteria are responsible for this type of diarrhea. Eating food that has been stored at room temperature for more than two hours is an important cause of Bacillus cereus infection. The onset of symptoms occurs anywhere between 6 and 15 hours after taking the food.
Both the types of toxins are heat-labile, i.e., they are not destroyed by heat. Also, the symptoms usually resolve within a day of onset.
2. Extragastrointestinal Symptoms
When the bacillus cereus comes in direct contact with wounds and the bloodstream, there is a risk of a severe type of infection.
The extraintestinal manifestations of Bacillus cereus infection are:
The risk of developing extraintestinal complications is further increased in the following conditions:
How Can We Diagnose Bacillus Cereus Infection?
Bacillus cereus infection can be diagnosed by assessing patients' vomitus samples or feces. Isolations of strains or large numbers of the same serotype of Bacillus cereus in the food samples or samples of vomitus or feces help confirm the diagnosis. Serology tests are available for diagnosing the presence of the diarrheal toxin, while biological tests can detect both emetic and diarrheal toxins.
Vitreous fluid is assessed for the presence of Bacillus cereus bacteria to confirm the diagnosis of endophthalmitis, an extraintestinal infection. However, when this bacteria is present in the bloodstream, it is a more serious condition called bacteremia.
How Is Bacillus Cereus Infection Treated?
Bacillus cereus infection does not usually have a need for targeted therapy. Symptomatic treatment along with oral or intravenous rehydration is needed in most patients.
In case of extragastrointestinal infections like endophthalmitis, immediate medical intervention is necessary. Depending on the organism involved, the antibiotics are chosen. The Bacillus cereus is resistant to beta-lactam antibiotics, and hence these are not recommended in treating Bacillus cereus infections.
Since Bacillus cereus is resistant to antibiotics like Clindamycin and Erythromycin, they are not the recommended first-line drugs in most cases.
Administration of antibiotics is done through intravenous or intraocular routes when there is a severe risk of systemic infection.
The following antibiotics are recommended in Bacillus cereus infections:
What Are the Complications of Bacillus Cereus Infection?
Gastrointestinal symptoms usually do not cause severe symptoms. However, immunocompromised share a risk of developing fatal complications.
Following are the extraintestinal complications of Bacillus cereus infection:
What Is the Differential Diagnosis of Bacillus Cereus Infection?
Bacterial infection caused by other groups of bacteria like Salmonella, Vibrio cholerae, Escherichia coli, Shigella, Campylobacter, Clostridium difficile, and Yersinia enterocolitica.
Parasitic infections with Cyclospora, Entameba, Giardia, Microsporidium, and Cryptosporidium.
How Can We Prevent Bacillus Cereus Infection?
Maintain food at a temperature greater than 60°C or less than 4°C.
To destroy the vegetative cells, food should be reheated at a temperature above 74°C for 15 seconds.
However, food should be reheated at 121°C for about 80 minutes when the toxins are present, which is almost impossible. Therefore, preventing infection in the first place is important.
Leftovers should be rapidly cooled to less than 4°C to prevent contamination.
With adequate preventive measures, preventing the contamination of food by Bacillus cereus is possible. Food products should be handled, processed, and stored effectively. When you have vomiting and diarrhea, it is essential to contact your healthcare provider to identify the cause.
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