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

activate T cells to proliferate and secrete cytokines
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

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Microorganisms and Disease
A major difference between EHEC and EPEC is

EHEC possesses a type III secretion system and EPEC does not
EPEC passes through the placenta to infect the fetus and EHEC does not
EPEC rearranges host cell actin and EHEC does not
EHEC secretes a Shiga-like toxin and EPEC does not

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

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