Molecular Pathogenicity Studies of Enteric Bacteria 
on the epithelial cell surfaces as on the intestinal 
tissue of an infected child. Thus the expression of 
bundles by EPEC is induced by physical and 
chemical variables found near the epithelial cell 
surface, where the bacteria seem to colonize 
through their propensity to form a network link- 
ing one to another. We have elected to call these 
structures colony-forming bundles, or CFB. It 
now seems likely that the colony begins to form 
as the bacteria descend to the epithelial cell sur- 
face and that it therefore constitutes the EPEC 
infectious unit. 
The role hypothesized for CFB was corrobo- 
rated by two additional observations. First, dele- 
tion of genes from EPEC that are required for the 
production of CFB yielded mutant bacteria that 
were unable to form cell surface colonies. Sec- 
ond, antibodies to CFB substantially reduced the 
colony- forming capacity of EPEC strains. This lat- 
ter finding suggests the use of a CFB vaccine to 
prevent diarrhea. 
We determined the molecular structure of the 
CFB filaments. Remarkable similarities were 
found between their amino acid sequence and 
the sequences of fibrous appendages produced 
by a variety of pathogenic bacteria that infect mu- 
cous membranes, including the agents of cholera 
and gonorrhea. Thus the CFB appears to be a 
shared structural innovation by bacterial species 
that live on mucous membranes. 
Scanning electron micrograph of enteropathogenic Escherichia coli (EPEC ) growing on an epithe- 
lial cell and expressing colony -forming bundles. 
Research of Gary K. Schoolnik. 
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