bacillus species

Genus: Bacillus
The anthrax bacillus, Bacillus anthracis, was the first bacterium shown to be cause of a disease. In 1877, Robert Koch grew the organism in pure culture, demonstrated its ability to form endospores, and produced experimental anthrax by injecting it into animals.
General characteristic:-
1- Gram positive rods in old culture appear as gram negative, arranged in chain.
2- Motile by peritirchous flagella except B.anthracis (non motile).
3- Spore former bacteria.
4- B.anthracis capsulated (polypeptide) when isolated from tissue (specimen) appear irregular & fragmented when stained by poly- chrome methylene blue (Mac fadyean reaction).
5- Aerobic, catalase positive & have ability to liquefied gelatin.
6- They form pellicles in liquid media.
7- They can persist for years in dry earth and may remain viable for month in animal hides.
8- The virulence factors of B.anthracis are its capsule and three-component toxin, both encoded on plasmids.
Normal habitat:
- Found in infected animal.
- Spores are found in soil, vegetable, water ….. etc.
Medical important species:
• B. anthracis.
• B. cereus.
• B. subtilis.
• B. mycoides.
• B. mesentericus.
Pathogenicity:
(B. anthracis):
Anthrax is caused by Bacillus anthracis. Humans acquire the disease directly from contact with infected herbivores or indirectly via their products (zoonotic disease). The clinical forms include (Depending on the source and the site of infection)
1- Cutaneous anthrax (enter through damaged skin producing malignant pustule which usually ulcerates and surrounded by edema. (fatal septicemia & toxaemia )
2- Pulmonary anthrax:
Caused when inhalation large number of B. anthracis spores (wool sorter's disease).
3- Enteric anthrax:
Sever from of gastroenteritis with fever, abdominal pain and bloody diarrhea due to ingestion infected meat.


* B. cereus:
- Cause food poisoning. The toxin is produced when bacilli sporulate, usually in rice that have been cooked and then stored in warm temperatures.
- May cause opportunistic infection in immuno-compromised persons eg pneumonia, bacteraemia & wound infections, (haemolysis on B. A) .
* Diagnosis:
1- Specimens)
- Fluid aspirated from cutaneous lesions.
- Sputum.
- Stool, Blood for culture.
2- stain:
Form infected tissue.
- G+ve rod, large.
- Short chains.
- Motile except B. anthracis.
- Mc fadyean reaction.
- Fixation using potassium permanganate
3- Culture:
On Blood agr:
Produce large 2 – 5 mm in diameter, produce grey- white colonies, the colonies are non haemolytic.
- Slowly liquefies the gelatin.
- B. cereus N. L.F. rapidly liquefies gelatin.
- Mannitol egg- yolk phenol – Red polymyxin agar (selective media).
- B.anthracis ( Medusa head like)
Control:-
Anthrax: Control in animals is essential for control in humans. In endemic areas, animals that die suddenly should be handled cautiously and livestock should be vaccinated annually. A human vaccine is available for individuals in high-risk occupations. Anthrax is readily treated with antibiotics (e.g., penicillin, tetracycline, chloramphenicol, gentamicin, or erythromycin).
Other Bacillus Infections: Control is by good hygiene. Treatment is with non-ß-lactam antibiotics for Gram-positive bacteria. Food poisoning is controlled by adequate cooking, avoidance of recontamination of cooked food, and proper storage (efficient refrigeration).