SUMMARY: A genetic factor (designated Ent) responsible for enterotoxin production in six of 51 enterotoxigenic strains of of porcine origin could be transmitted to other strains of and to and by conjugation in mixed culture. A high proportion of organisms of the recipient strains in these cultures was found to have accepted Ent, which was probably a plasmid. The possession of Ent by an organism was a stable characteristic; no organisms were found to have lost it during either laboratory cultivation, acriflavine treatment, or residence in the alimentary tract of pigs and mice. Ent could be transmitted independently of F, R, Hly and K88 factors; the transfer factor responsible for its transmission closely resembled F and the transfer factors of + R factors and Hly. Ent organisms could not be differentiated from Ent ones, morphologically, culturally or antigenically. The oral administration of enterotoxin-containing bacteria-free culture fluid of an Ent strain of had no apparent ill effect on pigs, piglets and calves; neither did the fluid influence skin permeability. The transmission of Ent to and did not affect their pathogenicity. Three of four piglets given Ent organisms developed diarrhoea; three given Ent organisms of the same strain did not.


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