Bacillus anthracis

Food Safety October 29, 2010 Print Friendly and PDF

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 degrees C to 48 degrees C, with optimal growth at 28 degrees C to 35 degrees C. They can grow in a broad pH range of 4.9 to 9.3.

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About Bacillus anthracis

A photomicrograph demonstrating a positive Gram stain with Bacillus anthracis. Photo courtesy of CDC.


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, it recently 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

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

Cutaneous infection of Bacillus anthracis accounts for about 95 percent 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 percent to 50 percent 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 percent 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 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. 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, infections of B. anthracis require medical attention.

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.