Bacillus species are Gram-positive, aerobic, ubiquitous bacteria characterized by their ability to form resistant spore coats. About 48 known species exist in the genus Bacillus but only B. anthracis and B. cereus are associated with human disease. Bacillus species produce heat-resistant endosopores and have a growth range of 10°C to 48°C, with optimal growth at 28°C to 35°C. They can grow in a broad pH range of 4.9 to 9.3.

Bacillus anthracis causes the disease Anthrax in humans and animals via direct contact with infected carriers or by inhalation of spores. In rare instances, consumption of contaminated meats has led to foodborne illnesses associated with B. anthracis. Conversely, B. cereus causes the majority of foodborne illnesses attributed to Bacillus. Although the incidence of naturally acquired anthrax is extremely rare in the United States, the Centers for Disease Control and Prevention estimated that in the year 2001, 22 cases occurred. From 1993 to 1997, B. cereus was linked to 14 outbreaks and caused 691 reported cases of foodborne illness in the United States.

Because of recent acts of terrorism and the threats of bioterrorism, B. anthracis remains an organism for which control mechanisms are necessary. While the most efficient method of delivering this biological weapon would be via an airborne route, the contamination of foodstuffs and water sources is possible. With the Public Health Security and Bioterrorism Preparedness and Response Act of 2002 and as the government continually prepares and responds to the threat of bioterrorism, clinical microbiological laboratories could play key roles in the detection, identification, and control of B. anthracis.

Bacillus cereus and Bacillus anthracis

Bacillus cereus is a spore-forming, Gram-positive, anaerobic bacterium associated with food poisoning in humans. Food poisoning is a result of ingesting heat-stable toxins produced by the bacteria: either a toxin that causes vomiting or one that causes diarrhea. B. cereus is widespread in the soil, and in the food industry in such foods as herbs, spices, milk, and vegetables. The disease is transmitted from contaminated foods, improper food handling/storage, and improper cooling of cooked foods.

Bacillus anthracis is a Gram-positive, nonmotile, aerobic, spore-forming bacterial rod that produces toxins. Although anthrax is a disease that primarily affects herbivorous animals such as cattle, sheep, and horses, recently it has become a concern in humans. Infections associated with anthrax are transmitted to humans either by direct contact with an infected animal or person, by consumption of contaminated animal products, or by the inhalation of the toxins and the capsule produced by the spores. The three toxins required for disease are edema toxin, lethal toxin, and the protective antigen factor. These toxins can lead to serious health-related problems such as edema, necrosis, and hemorrhages.

Sources of infection are classified in three types: cutaneous infections, inhalation anthrax, and gastrointestinal anthrax. Oropharyngeal anthrax and intestinal anthrax may occur if contaminated food or drink, such as infected meat or milk, is ingested. Transmission may occur through infected livestock or contaminated animal products. Although person-to-person transmission is rare, it may occur if infectious discharges associated with cutaneous infection are spread.

Symptoms of Bacillus cereus and Bacillus anthracis

Two types of illness are associated with B. cereus. The most common is a diarrheal illness accompanied with abdominal pain. An incubation period of 4 to 16 hours is followed by symptoms lasting 12 to 24 hours.

The second type involves vomiting, often associated with ingestion of rice that is not properly refrigerated after cooking. This illness is characterized by vomiting and nausea that usually occur within 1 to 5 hours upon ingestion of the contaminated food. This is sometimes referred to as an intoxication.

Cutaneous infection of Bacillus anthracis accounts for about 95% of all human cases, followed by inhalation and gastrointestinal anthrax, which are rare. Cutaneous infections start when the organism enters the body via open skin wounds or abrasions, resulting in skin lesions. The first symptom is a pus-filled elevation on the skin, which then turns into an open ulcer. The most severe cases may result in septicemia (blood poisoning)and death.

Symptoms of gastrointestinal anthrax include pharyngeal lesions with a sore throat, swelling in the neck, or intestinal infection resulting in nausea, fever, severe abdominal pain, bloody diarrhea, and hemorrhages. These symptoms are similar to a Staphylococcus infection. There is a 25% to 50% fatality rate.

Inhalation anthrax is the most severe and results from inhalation of spores. The spores are small enough to enter lungs, germinate, and produce toxins, resulting in infection and a 90% fatality rate without treatment. Symptoms first resemble those associated with pneumonia: fever, chills, cough, headache, and malaise, followed by more serious symptoms such as hemorrhages and septic shock.

Those at Risk

Bacillus anthracis and B. cereus can infect anyone because illness may result from ingesting contaminated food. However, the immuno-compromised, the very young, and older adults may suffer from more serious side effects. Inhalation of B. anthracis spores affects those who handle contaminated animal products and sabotaged materials. Members of occupational risk groups who work directly with animals, such as laboratory personnel or veterinarians, may be at a higher risk for anthrax.

B. cereus and B. anthracis may pose a higher risk for those working in food preparation areas and in slaughterhouses. Intact tissues and meat from animals are sterile, but after the animals are slaughtered, they may become contaminated from the processing plant or from bacteria that grow on the hide or in the gut.

Generally, gastroenteritis symptoms from B. cereus resolve by themselves but may require medical intervention. Infections of B. anthracis require medical attention.

Additional Resources

www.cdc.gov/ncidod/dbmd/diseaseinfo/anthrax_t.htm [1]

www.cfsan.fda.gov/~ebam/bam-15.html [2]

www.amif.org/AMIchillinggrowth.pdf [3]

edis.ifas.ufl.edu/MB001 [4]

www.fsis.usda.gov/OPHS/microlab/mlgchp12.pdf [5]