DEVELOPMENT AND APPLICATION OF AN AEROSOL CHALLENGE METHOD FOR REPRODUCTION OF AVIAN COLIBACILLOSIS

We have developed a reliable aerosol challenge method for reproduction of avian colibacillosis. This method involves intranasal administrati on of infectious bronchitis virus (IBV) to 1-day-old birds followed by three aerosol administrations of E. coli at 3 to 4-day intervals. In four separate experiments there was no significant difference in virul ence for a single isolate of E. coli (E3) whereas four other held isol ates of E. coli ranged from highly virulent to avirulent, We also obse rved that the dominant E. coli population isolated from 1-day-old bird s in a hock of broiler breeders was highly virulent but that the domin ant E. coli population isolated from birds in the same flock 2 weeks l ater was avirulent. The dominant E. coli population isolated from 1-da y-old birds in this flock was sensitive to all of the antimicrobial ag ents tested whereas the dominant E. coli population in the 2-week-old birds was multiresistant. A previous study has shown that it is likely that the changed resistance pattern of the dominant E. coli populatio n in the hock was linked to the administration of antimicrobial agents .