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10 Cards in this Set

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  • Back
What are the 2 pathogenic species of G+ aerobic spore forming rods?
Bacillus anthracis
Bacillus cereus- gastroenteritis(food poison ing)
Bacillus anthracis is unique in that it is the only bacterium with a capsule composed of protein(poly-D- glutamic acid). TRUE/FALSE
What is the function of this capsule?
It discourages phagocytosis.
How does the bacillus spore become virulent?
Once it is , for example, introduced into the lungs, intestine, or a skin wound it germinates and makes toxins. the germination and expression of plasma encoded virulence factors(on plasmids (pXO1 and pXO2) is regulated by an increase in temperature to 37 degrees C, CO2 concentration and serum proteins. The spore is about 1-2um in size.
The spores are often phagocytized by macrophages in the skin, intestine or lung and then germinate becoming active (vegetative) G+ rods. TRUE/FALSE
TRUE. The bacteria are released from the macrophage, reproduce in the lymphatic system and then invade the bloodstream, (up to 10-100 million organisms/ml of blood.
Why does anthrax carry such a high mortality rate?
The release of exotoxin is the major reason why anthrax carries such a high mortality rate. These toxins are encoded on a plasmid called pXO1. The exotoxin contains 3 separate proteins, which by themselves are nontoxic, but together produce the systemic effects of anthrax.
What are the 3 toxins called?
1.-Edema factor(EF)-This is the active A subunit of this exotoxin and is a calmodulin-dependent adenylate cyclase. It increases cAMP, which impairs neutrophil function and results in massive edema.
2. protective antigen(PA) promotes entry of EF into phagocytic cells(similar to a B subunit) of the other A-B toxins.
3. lethal factor(LF)- is a zinc metalloprotease that inactivates protein kinase. It stimulates macrophage to release tumor necrosis factor alpha and interleukin 1-beta, which contribute to death. A 2nd plasmid pXO2, encodes 3 genes necessary for the synthesis of a poly glutamyl capsule. It inhibits phagocytosis.
Are vaccines available for this organism?
Individuals taking part in high risk activities(petting goats or cows in countries where the disease is rampant) and military personnel should be given a vaccine composed of the protective antigen(PA). Animals are vaccinated with living cultures attenuated by the loss of their antiphagocytic protein capsule.
How is Bacillus cereus different from B. anthrax?
B. cereus are motile, non-encapsulated and resistant to penicillin. It causes food poisoning. Its spores are deposited in food, where they survive the cooking process. the enterotoxin is released.
B. cereus can secrete 2 types of enterotoxins. What are they?
1. Heat labile toxin- it is similar to the enterotoxin of cholera and the LT from E. coli.
2. Heat stable toxin- produces a clinical syndrome similar to that of Staph aureus food poisoning. Since the food poisoning is caused by the preformed enterotoxin of B. cereus, antibiotic therapy will not alter the course of the patients symptoms.