Bacillus cereus, excluding biovar anthracis: Infectious substances pathogen safety data sheet

Section I – Infectious agent

Name

Bacillus cereus, excluding biovar anthracis

Agent type

Bacteria

Taxonomy

Family

Bacillaceae

Genus

Bacillus

Species

cereus

Synonym or cross-reference

Causative agent of Bacillus cereus foodborne illness, food poisoning, diarrheal syndrome, emetic syndrome, and gastroenteritis^{Footnote 1Footnote 2Footnote 3}.

Characteristics

Brief description

Bacillus cereus sensu stricto (hereafter referred to as B. cereus) is a Gram-positive, endospore-forming, rod-shaped (1-1.2 µm by 3-5 µm) facultative anaerobe, which occurs singly, paired, or in short chains^{Footnote 2Footnote 4Footnote 5Footnote 6}. B. cereus is a member of a bacterial group known as Bacillus cereus sensu lato, which also includes B. anthracis, B. thuringiensis, B. mycoides, B. pseudomycoides, B. weihenstephanensis, B. cytotoxicus, and B. toyonensis, as well as several newly described members identified through more recent genetic taxonomic analyses, such as B. gaemokensis, B. manliponensis, and B. bingmayongensis^{Footnote 2Footnote 7}. Although these bacteria display high levels of genetic similarity, they are each classified as unique species based on differences in morphological and physiological features and associated clinical manifestations resulting from infection^{Footnote 2}. The genome size of B. cereus strain 3A-ES consists of a single circular chromosome approximately 5,335 kb in size, with a G+C content of ~35% and 287 subsystems (sets of proteins that together implement a specific biological process or structural complex), of which the largest number are involved in metabolic processes, followed by protein processing, virulence, stress response, and defense^{Footnote 8}. Cells have peritrichous flagella for motility^{Footnote 2}. B. cereus produces central-to-terminal ellipsoid or cylindrical spores with appendages on its surface^{Footnote 3Footnote 9}. Psychrotrophic strains grow well at temperatures below 10°C, but not at 37°C^{Footnote 10}. Mesophilic strains grow well at 37°C but can also survive at temperatures below 10°C^{Footnote 2Footnote 10}.

Properties

Some B. cereus strains have a generation time as short as 12 minutes under optimal conditions^{Footnote 3}. B. cereus is able to persist in unfavourable conditions through the formation of endospores and biofilms^{Footnote 2}. Spores are generally resistant to heating, freezing, drying, and gamma-ray and ultraviolet radiation^{Footnote 2}. Relative to spores from other Bacillus spp., B. cereus spores have an increased hydrophobicity, which allows for strong adhesion to surfaces and foods^{Footnote 3}. Biofilms can form on abiotic surfaces and on living tissue but can also be in the form of floating pellicles^{Footnote 2}.

B. cereus strains produce up to six toxins, of which five are enterotoxins and one is an emetic toxin^{Footnote 5}. Enterotoxins include enterotoxin T (BceT), enterotoxin FM (EntFM), hemolysin BL (HBL), nonhemolytic enterotoxin (NHE), and cytotoxin K (CytK or hemolysin IV)^{Footnote 2}. Some B. cereus strains produce an emetic toxin called cereulide^{Footnote 4Footnote 11Footnote 12}. B. cereus also produces other virulence factors including mammalian membrane-damaging phospholipases and hemolysins^{Footnote 2}. Spores produce two metalloproteases, InhA and NprA, which are involved in escaping immune surveillance and promoting germination, allowing for establishment of infection in a host.

Section II – Hazard identification

Pathogenicity and toxicity

B. cereus strains vary in pathogenicity due to differences in toxin production^{Footnote 4}. Pathogenic strains primarily cause self-limiting foodborne illness (diarrheal type and/or emetic type), but can also cause other types of infections^{Footnote 3Footnote 5Footnote 11}. The diarrheal type of food poisoning occurs when vegetative B. cereus cells are ingested and produce enterotoxins in the small intestine. This illness, which is characterized by symptoms such as watery diarrhea, abdominal pain, fever, and vomiting, often lasts for 12-24 hours, or up to several days^{Footnote 3Footnote 4Footnote 5Footnote 13}. The emetic type of illness, caused by the ingestion of food contaminated with pre-formed cereulide, is characterized by vomiting, nausea, malaise, and diarrhea, and lasts for 6-24 hours^{Footnote 3Footnote 5Footnote 13}. In a small number of cases, symptoms from both types of illness can occur simultaneously since approximately 5% of strains produce both types of toxins^{Footnote 3}. B. cereus food poisoning rarely leads to complications and mortality; however, occasional fatalities have been reported, including three deaths caused by the necrotic enterotoxin CytK, and deaths due to ingestion of large amounts of the emetic toxin^{Footnote 3Footnote 14}.

B. cereus also occasionally causes local and systemic infections aside from food poisoning^{Footnote 15}. Extraintestinal infections include septicemia, endophthalmitis, pneumonia, endocarditis, meningitis, and encephalitis, particularly in immunocompromised individuals and neonates. Mortality occurs in approximately 10% of cases involving extraintestinal local or systemic infections, and in up to 21% of cases involving hospitalized individuals^{Footnote 15}. Several cases of fulminant infections have been reported in healthy individuals, with symptoms similar to those of anthrax due to infection with non-biovar anthracis B. cereus isolates harbouring B. anthracis toxin genes^{Footnote 15Footnote 16Footnote 17}. A few fatal cases associated with fulminant liver failure due to the emetic toxin have been reported^{Footnote 5Footnote 18Footnote 19}.

B. cereus can occasionally cause mastitis in bovines and goats^{Footnote 20}. Disease ranges from mild to severe^{Footnote 21}. In a British survey, B. cereus mastitis accounted for 0.3% of cases of mastitis^{Footnote 21}. Cows with mastitis experience symptoms including fever, loss of appetite, lethargy, bloodstained milk, uniformly bloody udder secretions, enlarged, painful, discoloured and hard udders, and the occasional presence of necrotic mammary gland tissue in milk^{Footnote 20Footnote 21}. Gangrenous mastitis may develop, leading to necrosis and sloughing of the involved quarter udder and bluish-purple discoloration of the skin. Lactation may be permanently reduced. Of 119 cases of bovine mastitis reported in New South Wales, the mortality rate was 12%^{Footnote 22}. Goats infected with B. cereus experience similar symptoms as infected cows. Prognosis for survival is good for goats with proper treatment^{Footnote 20}. Aside from mammary gland infections, B. cereus infections may also cause abortion^{Footnote 20}.

B. cereus may cause hemorrhagic disease in dromedary camels^{Footnote 23}. This may cause the development of fatal leukopenia. A case of abortion due to B. cereus has also been described in a dromedary camel^{Footnote 23Footnote 24}.

B. cereus is pathogenic to multiple aquatic animal species, including Chinese softshell turtles, where disease is characterized by hepatic congestion and enlarged spleen, resulting in high mortality^{Footnote 25}.

Epidemiology

B. cereus has a worldwide distribution and is ubiquitous in the environment^{Footnote 5}. Since many B. cereus food poisoning cases are caused by improper food handling, there is no particular distribution pattern within a country^{Footnote 5}. However, there are national differences in the proportions of outbreaks caused by B. cereus. Emetic type food poisoning is the more prevalent type of B. cereus food poisoning in the United Kingdom and Japan, while the diarrheal type is more common in North America and northern Europe^{Footnote 11Footnote 26Footnote 27}. B. cereus was previously recorded as the cause of 17.8% of all bacterial foodborne illnesses in Finland, 11.5% in the Netherlands, 0.8% in Scotland, 0.7% in England and Wales, 2.2% in Canada, 0.7% in Japan, and 15% in Hungary^{Footnote 27}. The number of reported cases is likely underestimated since many cases are mild and of short duration^{Footnote 2}.

The number of annual cases of B. cereus-specific food poisoning is estimated to be approximately 27,000 in the United States^{Footnote 28}. B. cereus outbreaks involve 2-140 cases per outbreak, with a median of 8 cases^{Footnote 29}. B. cereus is one of the microorganisms most frequently isolated from samples taken from large commercial kitchens^{Footnote 4}. Contamination rates of B. cereus spores in foods such as noodles, potatoes, and rice are as high as 88-100%, and 50-83% in cooked vegetables^{Footnote 30}.

Sporadic cases of bovine B. cereus mastitis occasionally occur in the United States, Australia, the United Kingdom, Egypt, and New Zealand^{Footnote 21Footnote 22Footnote 31Footnote 32}. Contaminated animal feed containing Brewer’s grains are often associated with bovine B. cereus infections^{Footnote 21}.

No specific population is particularly predisposed to B. cereus foodborne illness; however, reduced stomach acidity as occurs in the elderly and in those suffering from achlorhydria may be a risk factor^{Footnote 11Footnote 33}. Old age, the presence of surgical or traumatic wounds, the use of intravascular and/or indwelling devices, neoplastic disease, immunosuppression, alcoholism, illicit drug use, and/or underlying medical conditions may be risk factors for extraintestinal B. cereus infections^{Footnote 5Footnote 15}.

Host range

Natural host(s)

Humans and animals, including cows, goats, and camels are natural hosts^{Footnote 3Footnote 20Footnote 24}. Tiger frogs, insect larvae and chickens can also be infected^{Footnote 15Footnote 34Footnote 35Footnote 36}.

Other host(s)

Insect species including Greater wax moths (Galleria mellonella) and silkworms (Bombyx mori), and small animals such as mice, rabbits, and guinea pigs, have been used as animal models^{Footnote 37Footnote 38Footnote 39Footnote 40}.

Infectious dose

For the diarrheal type of food poisoning, the infectious dose is 10⁴-10⁹ B. cereus cells per gram of food, while 10⁵-10⁸ B. cereus cells per gram of food are required to generate sufficient toxicity to cause the emetic type of food poisoning^{Footnote 5}.

Incubation period

The incubation period for the diarrheal type of food poisoning is 8-16 hours post-ingestion of contaminated food, and 0.5-6 hours post-ingestion for the emetic type^{Footnote 5Footnote 6}. Illness usually resolves within 24 hours of symptom onset^{Footnote 3}.

Communicability

B. cereus foodborne illness results from ingestion of B. cereus-contaminated food products^{Footnote 15}. Nosocomial transmission of B. cereus is also possible and occurs due to the transmission of spores present on human skin, or to the formation of B. cereus biofilms on fomites such as medical devices and bedsheets^{Footnote 15}. Transmission of B. cereus by contact with mucous membranes or damaged skin is possible through wounds and indwelling medical devices. Animal infection occurs primarily from ingestion^{Footnote 20Footnote 23}. Mammary gland infection may occur through accidental entrance into the udder tissue when ingesting contaminated feeds, as well as following teat surgery, and from the use of contaminated syringes, teat tubes, or teat dilators^{Footnote 20}.

Section III – Dissemination

Reservoir

B. cereus can be found in the normal gastrointestinal flora of humans and animals^{Footnote 4}. In the environment, B. cereus cells and spores remain viable in decaying organic matter, growing plants, and in the guts of invertebrates in soil^{Footnote 3Footnote 11}. This environmental distribution results in the contamination of foods, especially those of plant origin, including rice, pasta, vegetables, and spices, and in the contamination of pasteurized milk, meat, and eggs^{Footnote 3}.

Zoonosis

Food poisoning resulting from the ingestion of B. cereus-contaminated animal by-products is classified as foodborne zoonosis^{Footnote 41}.

Vectors

None.

Section IV – Stability and viability

Drug susceptibility/resistance

B. cereus strains are generally susceptible to imipenem, chloramphenicol, gentamicin, tetracycline, rifampin, linezolid, fluroquinolones (i.e., ciprofloxacin, gatifloxacin, levofloxacin, and moxifloxacin), and aminoglycosides (i.e., vancomycin, erythromycin, and daptomycin)^{Footnote 42}.

Due to beta-lactamase production, some B. cereus isolates are resistant to beta-lactams such as penicillins, oxacillins, and cephalosporins^{Footnote 15Footnote 42}. Some isolates are also resistant to erythromycin, tetracycline, carbapenem, clindamycin, cefazolin, cefotaxime and trimethoprim-sulfa-methoxazole^{Footnote 42Footnote 43}. Antibiotic resistance is highly variable depending on the isolate.

Susceptibility to disinfectants

Glutaraldehyde is capable of inactivating B. cereus cells (200 to 1000 mg/L for 30 minutes) and has partial activity against biofilms (200 mg/L for 30 minutes)^{Footnote 44}. Bacillus spores can be killed by a 3 hour treatment with ≥2% aqueous solutions of glutaraldehyde, buffered to pH 7.5–8.5 with sodium bicarbonate, and by a 1-hour exposure to 10% hydrogen peroxide^{Footnote 45}.

Physical inactivation

Pulsed electric fields can inactivate and reduce the number of B. cereus cells when suspended in 0.15% NaCl^{Footnote 46}. Although spores are relatively resistant to heat, cellular damage to the membranes and ribosomes is induced by exposure to moist heat (100°C) for 5 minutes^{Footnote 47}. Cooking meat at 70°C for 2 minutes is sufficient to significantly reduce the number of B. cereus vegetative cells^{Footnote 48}. Gamma irradiation at a dose of 2-5 kilograys (kGy) is required to inactivate B. cereus vegetative cells^{Footnote 49}. A combination of slightly acidic electrolyzed water (SAEW), mild heat (60°C), and ultrasound greatly collapses and disrupts B. cereus biofilms^{Footnote 50}.

Survival outside host

B. cereus, which is saprophytic, is ubiquitous in soil and on vegetation^{Footnote 40}. As B. cereus spores are generally resistant to acidic environments, proteolysis, and heat, they may survive thermal food processing and pasteurization^{Footnote 2Footnote 3Footnote 11}. In hospital settings, spores and biofilms can be found on human skin and abiotic surfaces such as medical devices and linens^{Footnote 15}.

Section V – First aid/medical

Surveillance

B. cereus can be identified by growing and isolating the bacterium at 37°C on B. cereus growth media such as MEYP (mannitol, egg yolk, polymyxin B) agar, PEMBA (polymyxin B, egg yolk, mannitol, bromothymol blue agar), and BCM (B. cereus medium)^{Footnote 5Footnote 51}. Immunological assays, PCR, and biological tests can detect the presence of B. cereus enterotoxins^{Footnote 5Footnote 27}.

Note: The specific recommendations for surveillance in the laboratory should come from the medical surveillance program, which is based on a local risk assessment of the pathogens and activities being undertaken, as well as an overarching risk assessment of the biosafety program as a whole. More information on medical surveillance is available in the Canadian Biosafety Handbook (CBH).

First aid/treatment

B. cereus food poisoning usually resolves quickly without treatment^{Footnote 4}. Appropriate antibiotic therapy and supportive care can aid in treating infected individuals, if required^{Footnote 19}. Fluid administration is recommended for severe diarrhea or vomiting. The early administration of antibiotics has been successful in preventing the progression of systemic infections and bacteremia^{Footnote 52}. Bovine mastitis may be treated with intra-mammary antibiotic therapy^{Footnote 21}.

Note: The specific recommendations for first aid/treatment in the laboratory should come from the post-exposure response plan, which is developed as part of the medical surveillance program. More information on the post-exposure response plan can be found in the CBH.

Immunization

No vaccine is currently available.

Note: More information on the medical surveillance program can be found in the CBH, and by consulting the Canadian Immunization Guide.

Prophylaxis

No known post-exposure prophylaxis.

Note: More information on prophylaxis as part of the medical surveillance program can be found in the CBH.

Section VI – Laboratory hazard

Laboratory-acquired infections

Only one case of B. cereus-associated laboratory-acquired infection has been reported; this case occurred in a research laboratory and was suspected to have been caused by contamination of a hand wound^{Footnote 53}.

Note: Please consult the Canadian Biosafety Standard (CBS) and CBH for additional details on requirements for reporting exposure incidents. 

Sources/specimens

Human stool, soil, and food specimens^{Footnote 3Footnote 42Footnote 54}.

Primary hazards

Ingestion of infectious material, exposure to infectious material on fomites, and exposure of mucous membranes/damaged skin to infectious material^{Footnote 2Footnote 3Footnote 4Footnote 15Footnote 53}.

Special hazards

None.

Section VII – Exposure controls/personal protection

Risk group classification

B. cereus is a Risk Group 2 Human Pathogen and a Risk Group 2 Animal Pathogen^{Footnote 55}.

Containment requirements

Containment Level 2 facilities, equipment, and operational practices outlined in the CBS for work involving infectious or potentially infectious materials, animals, or cultures.

Protective clothing

The applicable Containment Level 2 requirements for personal protective equipment and clothing outlined in the CBS are to be followed. The personal protective equipment could include the use of a labcoat and dedicated footwear (e.g., boots, shoes) or additional protective footwear (e.g., boot or shoe covers) where floors may be contaminated (e.g., animal cubicles, PM rooms), gloves when direct skin contact with infected materials or animals is unavoidable, and eye protection where there is a known or potential risk of exposure to splashes.

Note: A local risk assessment will identify the appropriate hand, foot, head, body, eye/face, and respiratory protection, and the personal protective equipment requirements for the containment zone and work activities must be documented.  

Other precautions

A biological safety cabinet (BSC) or other primary containment devices to be used for activities with open vessels, based on the risks associated with the inherent characteristics of the regulated material, the potential to produce infectious aerosols or aerosolized toxins, the handling of high concentrations of regulated materials, or the handling of large volumes of regulated materials.

Use of needles and syringes to be strictly limited. Bending, shearing, re-capping, or removing needles from syringes to be avoided, and if necessary, performed only as specified in standard operating procedures (SOPs). Additional precautions are required with work involving animals or large scale activities.

Additional information

For diagnostic laboratories handling primary specimens that may contain B. cereus, the following resources may be consulted:

• Human Diagnostic Activities Biosafety Guideline
• Local Risk Assessment Biosafety Guideline

Section VIII – Handling and storage

Spills

Allow aerosols to settle. Wearing personal protective equipment, gently cover the spill with absorbent paper towel and apply suitable disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time with disinfectant before clean up (CBH).

Disposal

All materials/substances that have come in contact with the regulated materials to be completely decontaminated before they are removed from the containment zone or standard operating procedures (SOPs) to be in place to safely and securely move or transport waste out of the containment zone to a designated decontamination area / third party. This can be achieved by using decontamination technologies and processes that have been demonstrated to be effective against the regulated material, such as chemical disinfectants, autoclaving, irradiation, incineration, an effluent treatment system, or gaseous decontamination (CBH).

Storage

The applicable Containment Level 2 requirements for storage outlined in the CBS are to be followed. Primary containers of regulated materials removed from the containment zone to be labelled, leakproof, impact resistant, and kept either in locked storage equipment or within an area with limited access.

Section IX – Regulatory and other information

Canadian regulatory information

Controlled activities with B. cereus require a Pathogen and Toxin licence issued by the Public Health Agency of Canada.

The following is a non-exhaustive list of applicable designations, regulations, or legislations:

• Human Pathogens and Toxins Act and Human Pathogens and Toxins Regulations                                                
• Health of Animals Act and Health of Animals Regulations
• Transportation of Dangerous Goods Act and Transportation of Dangerous Goods Regulations

Last file update

March, 2023

Prepared by

Centre for Biosecurity, Public Health Agency of Canada.

Disclaimer

The scientific information, opinions, and recommendations contained in this Pathogen Safety Data Sheet have been developed based on or compiled from trusted sources available at the time of publication. Newly discovered hazards are frequent and this information may not be completely up to date. The Government of Canada accepts no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information.

Persons in Canada are responsible for complying with the relevant laws, including regulations, guidelines and standards applicable to the import, transport, and use of pathogens in Canada set by relevant regulatory authorities, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment and Climate Change Canada, and Transport Canada. The risk classification and related regulatory requirements referenced in this Pathogen Safety Data Sheet, such as those found in the Canadian Biosafety Standard, may be incomplete and are specific to the Canadian context. Other jurisdictions will have their own requirements.

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