has neurotoxic activity causing paralysis and death in experimental
animals and is an enterotoxin capable of causing fluid accumulation in
ligated rabbit ileal loops. As an enterotoxin, it appears unrelated to
cholera toxin since it does not stimulate adenylate cyclase or cross-react
with antibodies to cholera toxin. Its role in the pathogenesis of shigellosis
is unclear since strains incapable of producing Shiga toxin remain
pathogenic. EnteroinvasiveE. colicauses a similar syndrome but does
not produce Shiga toxin.
Some authors have linked the enterotoxin activity of Shiga toxin with
the watery diarrhoea which often precedes dysentery. Interestingly, a
similar sequence of watery diarrhoea with supervening bloody diarrhoea
is seen with enterohaemorrhagic E. coli.This organism, which both
colonizes the epithelial surface in the colon and multiplies in thelamina
propria, produces a number of Shiga-like toxins, sometimes known as
verotoxins because of their activity against Vero cells in culture.
Common features have been identified among the various diarrhoea-
causing toxins and a number of bacterial exotoxins important in other
diseases such as diphtheria. Each consists of five, linked B units which
are able to bind to the target cell and facilitate transport of the active A
unit into the cell.
Having discussed some of the general features of foodborne diseases,
in the next chapter we will look more closely at some of the bacterial
agents responsible for them.
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