Genetic labeling of an Ent plasmid that encodes heat-stable enterotoxin of enterotoxigenic Escherichia coli isolated from patients.

Ent plasmids of enterotoxigenic Escherichia coli that encode heat-stable enterotoxin (ST) and both ST and heat-labile enterotoxin (LT) were labeled with a kanamycin- and an ampicillin-resistance transposon, respectively. These transposons were kept stably in the respective Ent plasmids. By monitoring antibiotic resistance we could easily select strains carrying Ent plasmids. Strains carrying the labeled plasmids produced enterotoxins that were immunologically indistinguishable from those produced by the parent strains. Moreover the strain carrying a labeled ST-Ent plasmid produced 16 times more ST than the parent strain.