Microorganisms and Disease
Type III secretion systems are used to inject "effector" proteins directly into a host cell. Salmonella uses a type III secretion system to help the pathogen to

survive within macrophages
secrete LT (heat labile toxin) and ST (heat stable toxin) into the lumen of the intestine
survive the acid pH of the stomach
activate T cells to proliferate and secrete cytokines

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Microorganisms and Disease
The "A" subunit of diphtheria toxin

binds host cell receptors found on heart cells
cause ADP ribosylation of a factor involved in protein synthesis
forms cAMP that leads to fluid accumulation
lysis macrophages with the release of cytokines

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Microorganisms and Disease
Cholera toxin is an A-B type toxin in which the B portions bind to a receptor on a host cell and the A portion enters the cell to cause

ADP ribosylation of a G protein that locks it into an active form that stimulates adenylate cyclase to make cAMP
ADP ribosylation of guanylate cyclase that stimulates production of cGMP
ADP ribosylation of adenylate cyclase that stops production of cAMP
cleavage of rRNA that results in disruption of ribosome function

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