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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Microorganisms and Disease
The influenza vaccine is administered each year because

mutations in the viral hemagglutinin may allow the virus to evade the immune response elicited by previous vaccines
None of these
the vaccine is sufficiently toxic to make it necessary to administer only a small amount at any one time
it is a polysaccharide vaccine that does not confer long-term protection

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Microorganisms and Disease
A major difference between EHEC and EPEC is

EHEC secretes a Shiga-like toxin 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 possesses a type III secretion system and EPEC does not

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