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
the vaccine is sufficiently toxic to make it necessary to administer only a small amount at any one time
None of these
it is a polysaccharide vaccine that does not confer long-term protection

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Microorganisms and Disease
The "A" subunit of diphtheria toxin

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

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Microorganisms and Disease
A major difference between EHEC and EPEC is

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
EHEC secretes a Shiga-like toxin and EPEC does not

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