Tween is a surfactant which is routinely used in immunoassays such as
ELISA and western blots. It disrupts weak non-specific protein-protein
interactions which cause high background.
ETEC infections are treated symptomatically if at all. In a healthy
adult, ETEC cause nothing more than diarrhea, and are really just a
nuisance. In children, rehration therapy is recommended to prevent
dehydration and electrolyte imbalances.
I'm not familiar with TCBS agar.