Spore forming gram positive Bacilli General characteristics



Download 4.36 Mb.
Page1/2
Date21.06.2018
Size4.36 Mb.
  1   2
Spore forming gram positive Bacilli

*General characteristics

1-Gram positive spore forming bacilli.

2- These includes two genus Bacillus and Clostridium species .

3-These bacilli are ubiquitous ,and because they form spores they can survive in the environment for many years.

4-Bacilli species are aerobes ,whereas Clostridia are anaerobes .

5-Not all species of Bacillus can cause disease ,however, there are few species cause important disease in humans e.g.Anthrax,that are caused by Bacillus anthracis ,which also cause disease in animal and occasionally in humans ,and it is a major cause of bioterrorism.



6-The genus Clostridium is extremely heterogeneous and more than 190 species have been described ,Clostridia cause several important toxin –mediated diseases.



*A*Bacillus species .

*General characteristic :

1-Large ,gram positive rods occurring in chains .

2-Most members of this genus are saprophytic organisms prevalent in soil ,water ,and air and on vegetation ,such as Bacillus cereus and Bacillus subtitis.

3- some of them are insect pathogen.

4-B.cereus can grow in foods and produce an enterotoxin or an emetic toxin and cause food poisoning.

5-B.anthracis ,which cause anthrax ,is the principal pathogen of the genus.

6-The spores of these organisms are resistant to environmental changes, withstand dry heat and certain chemical disinfectants for moderate periods, and persist for years in dry earth.

7-Animals products contaminated with anthrax spores can be sterilized by autoclaving.

*1*Bacillus anthracis

*Pathogenesis.

-Anthrax is primarily a disease of herbivores –goats,sheep,cattle,horses ,etc.

-Humans become infected incidentally by contact with infected animals or their products.

-In animals the portal of entry is the mouth and the gastrointestinal tract.

-In humans ,the infection is usually acquired by the entry of spores through injured skin (cutaneous anthrax)or rarely the mucous membranes(gastrointestinal anthrax)or by inhalation of spores into the lung(inhalation anthrax)

-The spores germinate in the tissue at the site of entry ,and growth of the vegetative organisms result in formation of a gelatinous edema and congestion.

-B.anthracis that does not produce a capsule is not virulent and does not induce anthrax in test animals

-The poly –D-glutamic acid capsule is antiphagocytic

-Anthrax toxin is made up of three proteins: protective antigen(PA), edema factor(EF),and lethal factor(LF )

-Protective antigen binds to specific cell receptor and mediate entry of EF and LF into the cell.

-EF+PA it forms a toxin known as edema toxin.

-LF+PA it forms a toxin known as lethal toxin. Which is a major virulence factor and cause of death in infected animals and humans.

-In inhalation anthrax (wool sorter disease ),the spores from the dust of wool,hair,or hides are inhaled ,phagocytosed in the lung transported by the lymphatic to the mediastinal lymph nodes, where germination occurs .

-This is followed by toxin production and the development of hemorrhagic mediastinitis and sepsis ,which are usually fatal.

*clinical findings

-In humans ,approximately 95% of cases are cutaneous anthrax and 5% are inhalation.





Share with your friends:
  1   2


The database is protected by copyright ©dentisty.org 2019
send message

    Main page