richia coli (EPEC) and Vibrio cholerae (the agent 
of Asiatic cholera). EPEC, a significant cause of 
childhood diarrhea, grows as free-living, isolated 
bacteria in contaminated water, but when ingested 
it rapidly adopts a colonial mode of growth and 
forms discrete colonies attached to intestinal mu- 
cous membranes. New surface structures form on 
the bacterial surface when it arrives in the intestinal 
environment, and these small filaments entwine to 
bind the bacteria into groups, or colonies. The sig- 
nals that effect this change are under study. The 
V. cholerae organism is under study to determine 
how the organism has evolved its ability to live in 
waters with salinity that varies seasonally. The an- 
cestral cholera toxin genes that permit the persis- 
tence of the organism in brackish water between 
epidemics may have acquired a new role as the prin- 
cipal virulence determinants of the bacteria. 
16 
