Anthrax bacilli vs Anthracoid bacilli- 25 Differences


Anthrax and anthracoid bacilli are two types of bacteria that belong to the genus Bacillus. They are gram-positive, rod-shaped, spore-forming, and aerobic organisms found in soil and animal products. However, they have different characteristics and pathogenicity that distinguish them.

Anthrax bacilli, also known as Bacillus anthracis, are the causative agents of anthrax, a severe and potentially fatal disease that affects humans and animals. Anthrax bacilli can form endospores highly resistant to heat, chemicals, and desiccation. These endospores can survive for long periods in the environment and can be inhaled, ingested, or inoculated through skin wounds. Depending on the route of infection, anthrax bacilli can cause different forms of disease, such as:

  • Cutaneous anthrax: The most common and least severe form of anthrax, characterized by a painless black ulcer (eschar) at the site of infection, accompanied by fever, headache, and lymphadenopathy.
  • Gastrointestinal anthrax is a rare but more severe form of anthrax caused by ingesting contaminated food or water. It manifests as abdominal pain, nausea, vomiting, diarrhea, and bleeding.
  • Inhalational anthrax: The most lethal form of anthrax, caused by inhalation of aerosolized endospores. It presents flu-like symptoms followed by severe respiratory distress, shock, and death.
  • Anthrax meningitis: A complication of any form of anthrax involving the spread of the bacteria to the central nervous system. It results in severe headaches, neck stiffness, confusion, seizures, and coma.

Anthrax bacilli can be diagnosed by culture, microscopy, or molecular methods. They can be treated with antibiotics such as penicillin, doxycycline, or ciprofloxacin. However, early diagnosis and treatment are essential to prevent mortality. Anthrax can also be controlled by vaccination and proper handling of animal products.

Anthracoid bacilli are a group of bacteria that resemble anthrax bacilli in morphology and staining properties. They include Bacillus subtilis, Bacillus cereus, Bacillus licheniformis, and Bacillus megaterium. They are generally considered non-pathogenic or opportunistic pathogens that rarely cause human disease. However, they differ from anthrax bacilli in many ways, as follows:

  • Anthracoid bacilli do not form capsules around their cells, unlike anthrax bacilli, which produce a thick capsule composed of poly-D-glutamic acid.
  • Anthracoid bacilli do not produce lecithinase (phospholipase C), an enzyme that degrades lecithin in cell membranes and causes hemolysis on blood agar plates. Anthrax bacilli multiply lecithinase, which gives them a characteristic halo effect on blood agar plates.
  • Anthracoid bacilli have different biochemical reactions and growth requirements than anthrax bacilli. For example, anthracoid bacilli can grow on MacConkey agar (a selective medium for gram-negative bacteria), while anthrax bacilli cannot.
  • Anthracoid bacilli have different antigenic structures than anthrax bacilli. For example, anthracoid bacilli do not have the protective antigen (PA), lethal factor (LF), and edema factor (EF) components that make up the anthrax toxin.
  • Anthracoid bacilli have different virulence factors than anthrax bacilli. For example, Bacillus cereus produces enterotoxins that cause food poisoning symptoms such as diarrhea and vomiting.

Anthracoid bacilli can be distinguished from anthrax bacilli by various laboratory tests such as capsule staining, lecithinase, motility, and serological tests. They can also be identified by molecular methods such as PCR or sequencing. Anthracoid bacilli are usually susceptible to antibiotics and do not require specific treatment unless they cause infection.

In conclusion, anthrax and anthracoid bacilli are two types of bacteria that share some similarities but differ in their morphology, physiology, and pathogenicity. Various laboratory methods can differentiate them and should be cautiously handled to prevent misdiagnosis or contamination.