Escherichia coli contains plasmids coding for heat-stable b, other enterotoxins, and antibiotic resistance.

Plasmid DNAs obtained from 18 Escherichia coli isolates that hybridized with the heat-stable b (ST-b) enterotoxin gene probe were examined by Southern blot analysis for genes coding for heat-labile, ST-a, and ST-b enterotoxins with specific radiolabeled DNA probes. Four E. coli isolates contained plasmids coding for both heat-labile and ST-b enterotoxins, and one isolate contained a plasmid coding for ST-a and ST-b. Five of 11 isolates of antibiotic-resistant enterotoxigenic E. coli isolates containing ST-b-coding DNA transferred a plasmid coding for both antibiotic resistance and ST-b to E. coli K-12, suggesting that the widespread use of antibiotics could increase the distribution of genes coding for ST-b.