Bacillus

The natural habitat of Bacillus anthracis, a Gram-positive, sporing, obligate aerobic rod bacterium, is the soil. The organism causes anthrax infections in animals. Human infections result from contact with sick animals or animal products contaminated with the spores. Infections are classified according to the portal of entry as dermal anthrax (95% of cases), primary inhalational anthrax, and intestinal anthrax. Sepsis can develop from the primary infection focus. Laboratory diagnosis includes microscopic and cultural detection of the pathogen in relevant materials and blood cultures. The therapeutic agent of choice is penicillin G.

The genera Bacillus and Clostridium belong to the Bacillaceae family of sporing bacteria. There are numerous species in the genus Bacillus (e.g., B. cereus,

B. subtilis, etc.) that normally live in the soil. The organism in the group that is of veterinary and human medical interest is Bacillus anthracis.

Bacillus anthracis (Anthrax)

Occurrence. Anthrax occurs primarily in animals, especially herbivores. The pathogens are ingested with feed and cause a severe clinical sepsis that is often lethal.

Morphology and culturing. The rods are 1 µm wide and 2-4 µm long, nonflagellated, with a capsule made of a glutamic acid polypeptide. The bacterium is readily grown in an aerobic milieu.

Pathogenesis and clinical picture. The pathogenicity of B. anthracis results from its antiphagocytic capsule as well as from a toxin that causes edemas and tissue necrosis. Human infections are contracted from diseased animals or contaminated animal products. Anthrax is recognized as an occupational disease.

Dermal, primary inhalational, and intestinal anthrax are differentiated based on the pathogen's portal of entry. In dermal anthrax, which accounts for 90-95% of human B. anthracis infections) the pathogens enter through injuries in the skin. A local infection focus similar to a carbuncle develops within two to three days. A sepsis with a foudroyant (highly acute) course may then develop from this primary focus. Inhalational anthrax (bioterrorist anthrax), with its unfavorable prognosis, results from inhalation of dust containing the pathogen. Ingestion of contaminated foods can result in intestinal anthrax with vomiting and bloody diarrheas.

Diagnosis. The diagnostic procedure involves detection of the pathogen in dermal lesions, sputum, and/or blood cultures using microscopic and culturing methods.

Therapy. The antimicrobial agent of choice is penicillin G. Doxycycline (a tetracycline) or ciprofloxacin (a fluoroquinolone) are possible alternatives. Surgery is contraindicated in cases of dermal anthrax.

Epidemiology and prophylaxis. Anthrax occurs mainly in southern Europe and South America, where economic damage due to farm animal infections is considerable. Humans catch the disease from infected animals or contaminated animal products. Anthrax is a classic zoonosis.

Prophylaxis involves mainly exposure prevention measures such as avoiding contact with diseased animals and disinfection of contaminated products. A cell-free vaccine obtained from a culture filtrate can be used for vaccine prophylaxis in high-risk persons.