Clostridium botulinum: Infectious substances pathogen safety data sheet

For more information on Clostridium botulinum, see the following:

• Diseases and conditions - Botulism

Section I – Infectious agent

Name

Clostridium botulinum

Agent type

Bacteria

Taxonomy

Family

Clostridiaceae

Genus

Clostridium

Species

botulinum

Synonym or cross-reference

Formerly known as Bacillus botulinus; causative agent of botulism^{Footnote 1}.

Characteristics

Brief description

C. botulinum are Gram-positive, anaerobic, rod-shaped, spore-forming bacilli that may occur singly, in pairs, or in chains and vary in size from 0.5–2.4 µm in diameter and 1.6–22.0 µm in length^{Footnote 2Footnote 3Footnote 4}. C. botulinum is divided into four distinct groups (I–IV) and seven serotypes (A-G) based on genetic and physiological characteristics, and the antigenicity of the produced neurotoxin: Group I (proteolytic; includes all type A strains and proteolytic strains of types B and F), Group II (non-proteolytic; includes all type E strains and non-proteolytic strains of types B and F), Group III (types C and D strains), and Group IV (Clostridium argentinense, formerly C. botulinum type G)^{Footnote 2Footnote 4Footnote 5}. Groups I and II are responsible for human disease, whereas Group III strains are implicated in disease in avian and some mammalian species^{Footnote 2Footnote 3}. C. botulinum Group I strain ATCC 3502 was the first to be sequenced; its genome has a low G+C content (28.2%) and comprises a chromosome (3.89 Mb) and a small plasmid (16.3 kb)^{Footnote 5}. The genomes of other Group I strains, as well as Group II strains, are highly similar; however, Group II strains have a slightly lower G+C content.

Properties

Characteristic of the genus Clostridium, C. botulinum forms oval-shaped, metabolically dormant endospores which are highly resistant to environmental stressors and allow persistence in unfavourable conditions^{Footnote 3}. Germination of the spores under favourable conditions results in vegetative growth of C. botulinum and production of BoNT (botulinum neurotoxins), the primary virulence factor and the causative agent of botulism^{Footnote 2Footnote 3}. BoNTs are divided into seven immunologically distinct serotypes (A–G)^{Footnote 2Footnote 3}. Serotypes A, B, E, and rarely F cause human botulism^{Footnote 3}. In addition to C. botulinum, C. argentinense (formerly C. botulinum type G), Clostridium butyricum, and Clostridium baratii can also produce BoNTs^{Footnote 2Footnote 3}.

Section II – Hazard identification

Pathogenicity and toxicity

Botulism is a rare but severe, and potentially fatal, neuroparalytic disease caused by BoNT produced during germination of C. botulinum spores^{Footnote 3}. BoNT binds to the neuromuscular junction and blocks excitatory synaptic transmission by inhibiting acetylcholine release, causing flaccid paralysis^{Footnote 6}. There are different forms of botulism depending on the route of exposure^{Footnote 2Footnote 3}. The most common types are foodborne, infant, and wound botulism, although iatrogenic, inhalation, and adult intestinal toxemia botulism have also been rarely reported^{Footnote 2Footnote 3}. Classic symptoms of botulism are commonly described as the four Ds: diplopia (double vision), dysarthria (difficulty with speech), dysphonia (altered voice), and dysphagia (difficulty swallowing)^{Footnote 2Footnote 7}. Left untreated, the disease can progress to fatal respiratory failure with a mortality rate between 40% and 50%^{Footnote 6Footnote 8}.

Foodborne botulism is the classic form of botulism and is caused by the ingestion of preformed BoNT in contaminated food^{Footnote 2}. Besides the four Ds, other symptoms include drooping eyelids (ptosis), slurred speech, and descending, symmetric flaccid paralysis which, if left untreated, develops into respiratory failure, leading to cardiac arrest and death^{Footnote 2Footnote 3Footnote 6}. Neurological symptoms may also be preceded by gastrointestinal symptoms, such as diarrhea, nausea, vomiting, and abdominal cramps^{Footnote 1Footnote 7}. The case fatality rate has significantly decreased in recent years and is now less than 5% as a result of improvements in clinical recognition, treatment, and food processing measures^{Footnote 2}.

Wound botulism occurs by contamination of a wound with spores from BoNT-producing Clostridium species in the environment and subsequent germination of these spores, followed by in situ production of BoNT and absorption into the bloodstream^{Footnote 2Footnote 6}. Symptoms are similar to foodborne botulism; however, there are no gastrointestinal symptoms^{Footnote 9}. The case fatality rate is 5-10%^{Footnote 9}.

Infant botulism results almost exclusively from spore ingestion and subsequent growth and toxin production in the intestine and affects infants under 1 year old^{Footnote 2Footnote 3}. The first clinical sign is usually constipation, but this disease has a wide spectrum of clinical severity, ranging from mild illness with gradual onset, to respiratory failure requiring mechanical ventilation^{Footnote 3Footnote 10}. BoNT absorption is minimal in infants, so disease is typically less severe than adult botulism; however, it may present with or progress to respiratory failure^{Footnote 6}. Infant botulism typically progresses for 1 – 2 weeks until stabilization is reached, and approximately 2-3 weeks are required for total recovery^{Footnote 6}. With supportive care, most infants with botulism recover in weeks or months without sequelae^{Footnote 6}. However, some cases have resulted in severe complications and long-term sequelae^{Footnote 11}. For example, in a study of 12 cases of infant botulism in the United States between 1977–1979, one of 12 infants was reported to be left with severe hypoxic ischemic encephalopathy from respiratory arrest en route to the hospital^{Footnote 11}. Further, patients with severe disease may develop bladder atony, which may lead to urinary retention, as well as Clostridioides difficile colitis, which can occur in infants with colonic stasis associated with botulism^{Footnote 12}. Other common infectious complications of infant botulism include otitis media, aspiration pneumonia, and urinary tract infections. Infants with botulism are lethargic, feed poorly, have a weakened cry, exhibit ptosis, and floppy neck, and may progress to muscular paralysis^{Footnote 3Footnote 9}. The case fatality rate is less than 1%^{Footnote 9Footnote 12}.

Adult intestinal botulism is a rare form of botulism caused by the intestinal colonization by C. botulinum, followed by in vivo BoNT production in a manner similar to infant botulism^{Footnote 2Footnote 3}. Symptoms are similar to foodborne and wound botulism^{Footnote 3}.

Inhalation botulism does not occur in nature but has been reported among laboratory workers exposed to aerosolized BoNT^{Footnote 3Footnote 7}. Inhalation botulism leads to neurological symptoms similar to those of foodborne botulism^{Footnote 9}.

Iatrogenic botulism results from injection of supratherapeutic concentrations of BoNT for cosmetic and/or therapeutic purposes and is characterized by muscle weakness along with the other classic symptoms of botulism^{Footnote 6Footnote 10}.

Epidemiology

Human outbreaks of botulism are sporadic and generally small and rare^{Footnote 3}. Outbreaks are commonly associated with foodborne botulism as a result of contaminated home-canned and commercially produced products^{Footnote 3}. Outbreaks of this disease type are reported worldwide^{Footnote 13}. Between 1920 and 2014, there were 197 outbreaks of foodborne botulism in the United States, Canada, Europe, Asia, Africa, and other countries, 55% of which occurred in the United States^{Footnote 13}. From 2006-2021, there have been 55 outbreaks of foodborne botulism in Canada^{Footnote 14}. From 1979 to 2019, 63 laboratory-confirmed cases of infant botulism were reported in Canada, for an average annual incidence of 4.3 cases per million live births during this time period^{Footnote 15}. From 2005 to 2017, 239 cases of wound botulism were reported in the United States, 93% of which were associated with injection drug use^{Footnote 16}. Adult intestinal toxemia botulism is very rarely reported and occurs sporadically; 33 cases have been described in the literature between 1986 and 2018^{Footnote 17}. Three of the cases were reported in Canada.

Injection drug use (primarily black tar heroin) and consumption of home-canned food represent risk factors for wound botulism and foodborne botulism, respectively^{Footnote 9}. In the case of adult intestinal botulism, colonization usually occurs because of severe interruption of the normal intestinal flora due to recent surgery, disease, or long-term broad-spectrum antibiotic use^{Footnote 3}. Risk factors for infant botulism include living in rural areas, having a parent who works with soil, and ingestion of honey within the first year of life^{Footnote 3Footnote 6}. Children over the age of 1 can ingest C. botulinum spores without colonization due to the development of their gut microbiota^{Footnote 15}. Pregnant patients with botulism may be at increased risk of respiratory failure^{Footnote 1}.

Botulism in animals, such as cattle, horses, and birds, occurs in large outbreaks with high mortality rates and large economic losses^{Footnote 3}. Animals can become infected after ingesting contaminated feed, prey, and maggots^{Footnote 3Footnote 18}.

Host range

Natural host(s)

Humans, birds, cattle, fish, mink, foxes, cats, dogs, and pigs are primary hosts^{Footnote 3}. Flies and their larvae are secondary hosts^{Footnote 18}.

Other host(s)

Mice and non-human primates can be experimentally infected^{Footnote 7}.

Infectious dose

The minimum infective dose of C. botulinum spores for human infants is unknown, but it may be as low as 10-100 spores based on estimates from exposure to spore-containing honey^{Footnote 19}.

Incubation period

In humans, the incubation period ranges from 12–72 hours for foodborne botulism^{Footnote 2}, 7–21 days for wound botulism^{Footnote 6}, 12–72 hours for inhalation botulism^{Footnote 6}, and 18–36 hours for infant botulism^{Footnote 2}.

Communicability

Human-to-human transmission of C. botulinum does not occur^{Footnote 2}. Foodborne botulism results from ingestion of contaminated food containing preformed BoNT, typically due to commercially processed and home-prepared foods that underwent improper processing, storage, and/or preservation^{Footnote 2Footnote 6}. Infant and adult intestinal botulism involve the ingestion of spores rather than preformed BoNT^{Footnote 3}. Wound botulism occurs due to exposure of damaged skin to contaminated surfaces such as soil, or through injection of black tar heroin^{Footnote 3}. Inhalation botulism results from inhalation of aerosolized BoNT^{Footnote 3}, whereas iatrogenic botulism results from injection of supratherapeutic concentrations of BoNT^{Footnote 6}; however, these forms of botulism represent intoxication rather than infection. Ingestion is considered the preferred mode of transmission as foodborne and infant botulism are the most common forms of botulism, although transmission by injection is also an important mode of transmission^{Footnote 2}.

Animal botulism typically occurs due to ingestion of contaminated feed or prey, or infection of wounds due to the ubiquity of C. botulinum spores in the environment^{Footnote 3}.

Section III – Dissemination

Reservoir

C. botulinum has been found in the gastrointestinal tracts of healthy birds, fish, and mammals^{Footnote 18}. Fish and pigs have been identified as healthy carrier animals of C. botulinum types E and B4, respectively^{Footnote 20}.

Zoonosis

While it is noted that botulism is not a communicable disease and that direct animal-to-human transmission does not occur, ingestion of contaminated foods prepared from healthy carrier animals of C. botulinum Group II strains, namely pigs (C. botulinum type B4) and fish (C. botulinum type E), presents a risk of animal-to-human transmission^{Footnote 20}.

Vectors

Necrophagous flies have been shown to act as mechanical vectors in avian botulism outbreaks^{Footnote 18}. These flies lay eggs on animal carcasses contaminated with BoNT, and feeding of larvae results in concentration of BoNT, followed by consumption of larvae by animals; this is referred to as the carcass-maggot cycle.

Section IV – Stability and viability

Drug susceptibility/resistance

Susceptible to penicillin, ampicillin, amoxicillin-clavulanic acid, moxifloxacin, metronidazole, clindamycin, cephalothin, cefoxitin, chloramphenicol, tetracycline, erythromycin, trimethoprim-sulfamethoxazole, rifampin, and vancomycin (with some strain variation)^{Footnote 21Footnote 22Footnote 23}. Resistant to cycloserine^{Footnote 23}.

C. botulinum was shown to be susceptible to cephalosporin antibiotics, including ceftriaxone, cefuroxime, cefotaxime, and cefepime; however, it is proposed that treatment with a cephalosporin may result in the development of more extensive and sustained paralysis^{Footnote 21}.

Susceptibility to disinfectants

NaCl concentrations between 5-10% are sufficient in preventing growth of C. botulinum, depending on the phenotypic group^{Footnote 3}. BoNTs are susceptible to disinfectants such as ethanol and 0.1% sodium hypochlorite^{Footnote 7}. C. botulinum spores are susceptible to 1% sodium hypochlorite^{Footnote 24}. Clostridium sporogenes spores, which are similar to those of C. botulinum, are susceptible to disinfectants containing 0.01% peracetic acid or 2.5% glutardialdehyde^{Footnote 25}. General sporicidal disinfectants include >0.05% wt/vol chlorhexidine diacetate, >0.05% wt/vol cetylpyridinium chloride, >0.4% wt/vol chlorocresol, >5% wt/vol cresol, and >0.02% wt/vol phenol, phenylmercuric nitrate (PMN)^{Footnote 26}.

Physical inactivation

Heat treatment at 121°C for 3 minutes at high pressure (termed "botulinum cook") is sufficient to inactivate C. botulinum spores^{Footnote 3Footnote 9}. Preformed BoNT in food can be inactivated through heating at 85°C for 5 minutes^{Footnote 3Footnote 6}. Irradiation at doses of 2.0–4.5 kGy and 1.0–2.0 kGy are effective to achieve a one-log reduction in spores of proteolytic and non-proteolytic C. botulinum strains, respectively, in frozen foods^{Footnote 9}. High-pressure processing (HPP) at 600–900 MPa combined with high temperatures (80–110°C) can inactivate C. botulinum spores, although the degree of inactivation is dependent on organism-related factors (e.g., type of bacterium, growth phase, inoculum dose, optimal growth temperature), food matrices (e.g., pH, water activity, physicochemical properties), and treatment conditions (temperatures, air, packaging, pressure fluid)^{Footnote 9}.

Survival outside host

C. botulinum spores survive well in soil, water and agricultural products and can persist in these environments for decades^{Footnote 18}. Sunlight inactivates BoNT within 1 to 3 hours^{Footnote 27}. Aerosolized BoNT is estimated to decay at a rate of 1–4% per minute^{Footnote 7}.

Section V – First aid/medical

Surveillance

Since botulism is a life-threatening condition, a rapid diagnosis is essential and requires testing to avoid misdiagnosis with other neurological diseases^{Footnote 10}. Treatment should not be delayed for confirmation of test results^{Footnote 3}. The mouse bioassay is the most reliable method for confirmation of diagnosis of botulism^{Footnote 3Footnote 28}. The enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) can also be used to detect BoNT or C. botulinum from patient samples^{Footnote 2Footnote 28}. If PCR is used, there is a possibility of detecting an organism that carries the BoNT-producing gene but does not express the toxin^{Footnote 28}.

Foodborne botulism can be diagnosed by the presence of BoNT in serum, stool, gastric aspirate or implicated food, or by culture of C. botulinum from a patient's gastric aspirate or stool in a clinical case^{Footnote 6Footnote 10Footnote 28Footnote 29}. Wound botulism can be diagnosed by the presence of BoNT in serum or through detection of a neurotoxin-producing Clostridium species from debrided tissue, wound swab sample, or anaerobic wound culture^{Footnote 10}. Infant and adult intestinal botulism can be diagnosed by demonstration of C. botulinum (or other neurotoxin-producing species) and/or toxins in a patient's stool^{Footnote 6}. Inhalation botulism can be diagnosed by detection of BoNT in serum^{Footnote 7}. Iatrogenic botulism should be suspected if the patient has recently received therapeutic injections of BoNT, which can be detected in serum or by single-fiber electromyography^{Footnote 6}.

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.

First aid/treatment

Individuals with suspected or diagnosed botulism may require supportive care with nutrition and respiratory support^{Footnote 6}. Botulism Antitoxin Heptavalent (BAT^®) is effective against all seven serotypes of botulism and should be used to treat all cases of botulism, except for infant botulism^{Footnote 3Footnote 30}. For foodborne botulism, gastric lavage, enemas, and the administration of a cathartic (sorbitol) may be considered if ingestion of the contaminated food is recent^{Footnote 1}. In the case of wound botulism, the wound should also be debrided and antibiotics, such as penicillin or metronidazole, should be administered following antitoxin treatment^{Footnote 6Footnote 10}. Antibiotics are not recommended for other forms of botulism due to the risk of exacerbating neurological symptoms and lysing vegetative C. botulinum cells, thereby releasing more BoNT^{Footnote 2Footnote 3Footnote 10}. BabyBIG^®, a human-derived immunoglobulin, is used to treat infant botulism; however, it is not approved for use in Canada and currently only available via the Health Canada Special Access Programme (SAP)^{Footnote 3Footnote 28Footnote 31}.

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 Canadian Biosafety Handbook.

Immunization

No vaccine currently available for humans^{Footnote 3}. As of 2018, two phase 2 clinical trials for vaccine candidates were completed, one of which was developed to replace the current BabyBIG^® formula^{Footnote 30}. Veterinary vaccines have been developed to protect cattle, sheep, mink, and horses^{Footnote 3}.

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

Prophylaxis

Administration of BAT^® within 48 hours of symptom onset may reduce the severity of disease and development of paralysis in all forms of botulism, except for infant^{Footnote 2Footnote 10}. Antitoxin should be administered to pregnant patients diagnosed with botulism^{Footnote 10}.

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

Section VI – Laboratory hazard

Laboratory-acquired infections

Pre-1970, three cases of inhalation botulism were reported in laboratory settings^{Footnote 7}. Three veterinary personnel were disposing rabbits and guinea pigs whose fur was coated with aerosolized BoNT/A; this serotype was subsequently detected in serum samples of the three individuals. Since then, there have been no documented cases of botulism in laboratory settings.

Note: Please consult the Canadian Biosafety Standard and Canadian Biosafety Handbook for additional details on requirements for reporting exposure incidents.

Sources/specimens

C. botulinum and/or BoNT can be found in blood, stool, vomit, gastric aspirates, wound exudates and swab samples, debrided tissue, skin lesions of heroin users, and sinus aspirates of patients with intranasal cocaine use^{Footnote 3Footnote 6Footnote 10}.

Primary hazards

Ingestion, contact with damaged skin or mucous membranes, and inhalation of aerosolized BoNT are the primary hazards associated with exposure to C. botulinum and/or BoNT^{Footnote 3Footnote 7}.

Special hazards

None.

Section VII – Exposure controls/personal protection

Risk group classification

C. botulinum is a Risk Group 2 Human Pathogen and a Risk Group 2 Animal Pathogen^{Footnote 32Footnote 33}.

Containment requirements

Containment Level 2 facilities, equipment, and operational practices outlined in the Canadian Biosafety Standard 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 Canadian Biosafety Standard 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, post mortem 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

The potential for exposure to BoNT and absorption after ingestion, or following contact with non-intact skin or mucous membranes, as well as formation of C. botulinum spores justify the use of a BSC or other primary containment devices for activities with open vessel; centrifugation to be carried out in sealed safety cups or rotors that are unloaded using a mechanism that prevents their release. Respiratory protection to be considered when BSC or other primary containment devices cannot be used; inward airflow is required for work involving large animals or large scale activities.

Use of needles and syringes are to be strictly limited. Bending, shearing, re-capping, or removing needles from syringes are 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.

For diagnostic laboratories handling primary specimens that may contain C. botulinum, 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 (Canadian Biosafety Handbook).

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 (Canadian Biosafety Handbook).

Storage

The applicable Containment Level 2 requirements for storage outlined in the Canadian Biosafety Standard 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 C. botulinum require a Pathogen and Toxin licence issued by the Public Health Agency of Canada (PHAC). C. botulinum is a terrestrial animal pathogen in Canada; therefore, importation of C. botulinum requires an import permit under the authority of the Health of Animals Regulations (HAR). The PHAC issues a Pathogen and Toxin Licence which includes a Pathogen and Toxin Licence and an HAR importation permit.

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
• Quarantine Act
• National notifiable disease (human)
• Annually notifiable disease (animal)

Last file update

June 2024

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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