An I Pilus-determining R Factor with Anomalous Compatibility Properties, Mobilizing a Gentamicin-resistance Plasmid

SUMMARY: An R factor complex, JR66, consisted of JR66a, a self-transmissible plasmid conferring resistance to streptomycin and kanamycin and capable of mobilizing JR66b: JR66b was a non-self-transmissible plasmid conferring resistance to gentamicin, streptomycin, tetracycline, chloramphenicol, kanamycin and sulphonamides. It was a member of compatibility group FII. JR66a, which determined I pili, was incompatible with members of two distinct groups, I and B. Plasmids of both these groups were shown to determine I pili.