Acquisition and Maintenance of Enterotoxin Plasmids in Wild-type Strains of Escherichia coli

Abstract

Enterotoxigenic E. coli (ETEC) strains may produce a heat-labile enterotoxin (LT) and/or a heat-stable enterotoxin (ST). Certain serogroups are represented more frequently than others in ETEC isolated from humans. The transfer of 3 plasmids encoding enterotoxin production (Ent) to 22 nontoxigenic E. coli strains of many different O:H serotypes was studied. The Ent plasmids encoded ST (TP276), or LT (TP277) or ST + LT (TP214); all carried antibiotic-resistance determinants. Some 21 recipient strains acquired TP214, 18 acquired TP277 and 14 acquired TP276. Strains of those serotypes to which ETEC in diarrheal studies commonly belong neither acquired nor maintained Ent plasmids with a higher frequency than strains of those serotypes to which ETEC rarely belong. The recipient strains, with 1 exception, all expressed ST, or LT, or ST and LT when they acquired the appropriate plasmid; a nonmotile strain belonging to O serogroup 88 expressed LT but failed to express ST when it acquired TP214 or TP277.