Naturally occurring plasmid carrying genes for enterotoxin production and drug resistance.

Escherichia coli strain 86, isolated from a piglet with diarrhea, carries plasmid-linked genes for resistance to tetracycline, streptomycin, and sulfonamides and for production of heat-labile and heat-stable enterotoxin. Results of (i) genetic experiments involving conjugal transfer and phage P1-mediated transduction and (ii) physical experiments involving electron microscopic examination of plasmid DNA and heteroduplex analysis show that a single conjugative plasmid carries the genes for drug resistance and production of enterotoxin.