Attempted Elimination of Plasmid‐determined Haemolysin, K88 Antigen and Enterotoxin from Escherichia coli Pathogenic for Pigs

The plasmid‐borne gene for haemolysin ( hly + ) was most easily cured with inhibitors of RNA transcription, whereas DNA inhibitors of replication were most effective against the determinant for K88 antigen ( K88 + ). Transitory removal of the enterotoxic determinant ( ent + ) was achieved with both RNA and DNA inhibitors. It is suggested that ent + might be chromosomally determined as well as plasmid‐borne in pathogens.