Spore-forming bacteria

Spore-forming bacteria
Some bacteria are capable of forming spores around themselves. They are Gram-positive and usually rod-shaped. Bacterial spores are made of a tough outer layer of keratin that is resistant to chemicals, staining and heat. The spore allows the bacterium to remain dormant for years, protecting it from various traumas, including temperature differences, the absence of air, water and nutrients. There are two medically-important genera of spore-forming bacteria are: Bacillus, whose species are aerobic spore formers of soils, and Clostridium, whose species are anaerobic spore formers of soils, sediments and the intestinal tracts of animals.
Bacillus
It is aerobic, G+ non-motile rods arranged in chains, spores are located in the center of the cell. Most members of this genus are saprophytic organisms prevalent in soil, water, and air and on vegetation. . Two species are considered medically significant:
-B.anthracis, which causes anthrax
- B.cereus which causes food poisoning similar to that caused by staphylococcus.
The other species of bacillus are:
- B.thuringiensis, is an important insect pathogen, and is sometimes used to control insect,
- B. subtilis it is a notable food spoiled and
- B. Stearothermophilus used for efficiency testing of an autoclave.





Clinical Manifestations
A- Anthrax
Anthrax zoonotic disease. Its primarily disease of herbivore, the portal of entry is the mouth and the gastrointestinal tract. Human acquire it as a result of contact with infected cattle and sheep. In human the disease takes one of three forms, depending on the route of infection:

1- Cutaneous anthrax
2-Intestinal anthrax
3-Pulmonary anthrax



1- Cutaneous anthrax, which accounts for more than 95% of cases worldwide. It is results from infection through the skin lesions. It is usually occurs through contamination of acute or a brasion. After a 2- to 3 day incubation period, small pimple or papule appears at the inoculation site. A surrounding ring of vesicles develops. Over the next few days, the central papule ulcerates, dries and surrounded by marked edema the lesion is painless that may extend to form the characteristic eschar. Pus and pain appear only if the lesion becomes infected by pyogenic organism. Similarly, marked lymphangitis and fever usually point to a secondary infection. If host defenses fail to contain the infection, however fulminating septicemia develops.
2- Intestinal anthrax result from ingestion of spores, usually in infected meat. The organisms probably invade the mucosa through a preexisting lesion.
3- Pulmonary anthrax, results from inhalation of spores. Inhaled spore is transported by alveolar macrophages to the mediastinal lymph nodes, where they germinate and multiply to initiate systemic disease.