Avian Colibacillosis: E. coli Serotype Infection

E. coli serotypes O78, O26, O55, and O44 obtained from local cases of avian colibacillosis as described above were enriched in trypticase soy broth (Oxoid) and incubated at 37°C for 24 h. The surface spread method was used to determine viable cells per mL of trypticase soy broth [20 (link)]. E. coli suspensions containing 10⁹ CFU/mL were prepared as previously described by Ateya et al. [21 (link)]. Infection with E. coli serotypes was achieved by oral administration of 0.5 mL of bacterial suspension to 7-day-old chicks using a syringe attached to a polyethylene tube. Birds were given a similar amount of sterile phosphate buffer saline as a negative control.