Type 1 and 5 secretion systems and associated toxins - Escherichia coli: Pathotypes and Principles of Pathogenesis - page 507

CONCLUSIONS
The T1SS and T5SS of E. coli are relatively simple pathways for the bacterium
to secrete a diverse range of virulence factors. Both pathways are capable of
secreting very large proteins (>3000 aa) with a wide range of virulence func-
tions including toxin, protease and lipase activity, adhesion to host cells and
the formation of biofilms. As both pathways require only a few genes, there
has been extensive horizontal gene transfer of virulence factors secreted via the
T1SS and T5SS, many of which reside on pathotype-specific plasmids. This
horizontal spread has allowed E. coli strains to quickly acquire and disperse an
arsenal of virulence factors.
As many of the virulence factors secreted by these two pathways are only
found in specific pathotypes of E. coli , they are ideal targets for vaccine devel-
opment. In addition, both pathways are currently being used to secrete or
display chimeric proteins and antigens for either mass production or attenuated
bacterial live vaccines.
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