Bacillus anthracis is a Gram‑positive, rod‑shaped bacterium that causes anthrax. It forms tough endospores that can remain dormant in soil for decades, and it was the first bacterium linked directly to a specific disease.
Explanation
The vegetative cells of B. anthracis are about 3–5 micrometres long and 1–1.2 micrometres wide and often grow in chains. Two plasmids, pXO1 and pXO2, carry genes that encode the anthrax toxin proteins and a poly‑D‑glutamic acid capsule. The capsule helps the bacterium avoid immune cells, while the toxins cause tissue damage and shock. Outside a host, the organism forms a central endospore that protects its DNA from heat, desiccation and disinfectants; spores can survive in soil for years. Within a susceptible animal or human, spores germinate, multiply and produce toxins. Infection typically occurs through contact with contaminated hides, wool or meat, inhalation of spores or, less commonly, ingestion. Cutaneous anthrax causes a characteristic black eschar on the skin; inhalational and gastrointestinal forms can be fatal without prompt treatment.
Clinical significance and control
Anthrax primarily affects grazing animals such as sheep and cattle, but humans can be infected through occupational exposure. Because spores are stable and can be disseminated as aerosols, B. anthracis has been used in biological warfare. Control measures include animal vaccination, proper disposal of animal carcasses and decontamination of contaminated materials. Antibiotics such as penicillin, ciprofloxacin and doxycycline are effective if given early. An anthrax vaccine adsorbed is available for people at high risk.
The bacterium remains important both as a model for studying host–pathogen interactions and as a concern for public health security.
Related Terms: Anthrax, Bacillus, Endospore, Capsule, Toxin