The immune response of turkeys to live attenuated vaccine for avian pathogenic Escherichia coli
(APEC) constructed from O78 strain was evaluated, where ninety-one-day old turkeys were vaccinated
twice with 3 weeks intervals. Other thirty turkeys were kept as non-vaccinated control. Birds were
challenged against homologous O78 and heterologous O1 and O2 pathogenic strains of E. coli using 107
CFU/0.2 ml/ turkey. Clinical and necropsy examinations revealed that vaccinated birds showed 96.7%
protection after homologous challenge while vaccinated birds were unable to withstand the heterologous
challenge. E. coli was recovered from vaccinated challenged turkeys at ratio ranged from13.3%-20%
from the heart blood, liver, spleen and bone marrow on the 8th day post homologous challenge while
these ratios were ranged from 53.3%-66.7% from vaccinated birds post heterologous challenge. So, the
vaccination studies performed here showed that live attenuated E. coli vaccine was protective against
homologous challenge with O78 strain but con not protect turkeys against heterologous challenge