Plasmid coding for aerobactin production and drug resistance is involved in virulence of Escherichia coli avian strains.

1. Strains of avian septicemic E. coli were examined for association among the determinants of drug resistance, the genes for aerobactin production and virulence. 2. In conjugation experiments, a single plasmid (100 Md) from a strain of septicemic E. coli (UEL 29) transferred to E. coli K12 pathogenicity for 1-day old chicks plus resistance to streptomycin and the ability to produce aerobactin and colicin. 3. Additional evidence for the association of R-plasmid and the production of aerobactin, colicin, resistance to sulfadiazine and pathogenicity was obtained by disassociation when all traits were lost simultaneously. 4. These data provide additional evidence for the importance of the aerobactin system for the pathogenicity of avian E. coli.