Bacillus cereus is a toxin-producing facultatively anaerobic gram-positive bacteria. The bacteria is commonly found in the environment, is often found in soil and vegetation, and can be present in foods. It can quickly multiply at room temperature. There are two main types of intestinal illnesses caused by B. cereus. One is diarrheal, and one leads more to nausea/vomiting. B. cereus has also been implicated in infections of the eye, respiratory tract, and in wounds. The pathogenicity of B. cereus, whether intestinal or nonintestinal, is intimately associated with the production of tissue-destructive exoenzymes. Among these secreted toxins are four hemolysins, three distinct phospholipases, an emesis-inducing toxin, and proteases.[1][2]

B. cereus illness is related to many foods - beef, turkey, rice, beans, vegetables. Specifically, the diarrheal illness is often related to meats, milk, vegetables, and fish. The emetic-type illness is most often associated with rice products, but it has also been associated with other types of starchy products such as potato, pasta, and cheese products. Some food-mixtures (sauces, puddings, soups, casseroles, pastries, and salads, have been associated with food-borne illness in general.[3][4]

Bacillus cereus is caused by the ingestion of food contaminated with either the enterotoxigenic B. cereus or with the emetic toxin. In non-gastrointestinal illness, reports of respiratory infections similar to respiratory anthrax have been attributed to B. cereus strains harboring B. anthracis toxin genes. 

The Centers for Disease Control (CDC) website states that there were 619 confirmed outbreaks of Bacillus-related poisoning from 1998 through 2015, involving 7385 illnesses. In this timeframe, there were 75 illnesses and three deaths due to confirmed Bacillus-related illness. The website states there were 19,119 outbreaks overall, and 373,531 illnesses. It refers to 14,681 hospitalizations and 337 deaths. These statistics refer to all Bacillus-related illness, and not just B. cereus related illness.[5][6]

The Bad Bug Book further breaks this down and states there are an estimated 63,400 episodes of B. cereus illness annually in the United States. In 2005, 2006, and 2007 there were 13 confirmed outbreaks and 37.6 suspected outbreaks during this period, involving over 1000 people.

All people are considered to be susceptible to B. cereus infection. Mortality is rare. The emetic enterotoxin has been found to be associated with a few cases of liver failure and death in otherwise healthy people. There is a newly found cytotoxin that has been associated with a B. cereus strain that caused one confirmed outbreak and three deaths. The infective dose or the number of organisms most commonly associated with human illness is 10^5 to 10^8, but pathogenicity arises from the preformed toxin, not from the bacteria themselves.

There are two types of food-borne B. cereus illness. In the first, contaminated food (many types of food, often left at room temperature) makes its way to the small intestine where the toxin, in this case, a large-molecular-weight protein, is released. This can lead to diarrhea, cramps, and sometimes nausea. Usually, vomiting is not present in this form of illness. Incubation for the first type is 6 to 15 hours. In the second type, affected food, most often starchy food, and classically, rice, contains a different type of toxin (cereulide, an ionophoric low-molecular-weight dodecadepsipeptide that is pH-stable and heat and protease-resistant). This toxin causes emetic-type B. cereus illness. The incubation period for this type is 30 minutes to 6 hours.

Endophthalmitis is a vision-threatening eye infection resulting from microbial infection of the inner eye. The hallmark of the ophthalmic lesion is a corneal ring abscess, which may be accompanied by rapid progression of pain, proptosis, chemosis, retinal hemorrhage, and perivasculitis. Systemic manifestations include fever, leukocytosis, and general malaise.

The non-hemolytic enterotoxin (NHE) from Bacillus cereus is an activator of the NLRP3 inflammasome and pyroptosis. [7]

The pathogenicity of B. cereus, whether inside or outside of the gastrointestinal (GI) tract, is associated with exoenzyme production. Among the secreted toxins are four hemolysins, three distinct phospholipases, an emesis-inducing toxin, and three pore-forming enterotoxins: hemolysin BL (HBL), nonhemolytic enterotoxin (NHE), and cytotoxin K. In the gastrointestinal tract (small intestine), vegetative cells, ingested as viable cells or spores, produce and secrete a protein enterotoxin and induce a diarrheal syndrome, whereas emetic toxin, a plasmid-encoded cyclic peptide (cereulide), is produced in food products and ingested as a formed toxin. In rabbit ligated ileal-loop assays, culture filtrates of enterotoxigenic strains induce fluid accumulation and hemolytic, cytotoxic, dermonecrotic, and vascular permeability activities in rabbit skin.

The enterotoxin is composed of a binding component (B) and two hemolytic components, designated HBL. Also, diarrheagenic in the gastrointestinal tract is a nonhemolytic three-component enterotoxin, designated NHE. The emetic toxin, which induces a vomiting syndrome, is synthesized in the contaminated food product, usually rice, pasta, or dairy products, in which B. cereus is growing and may represent a product of growth.