Detection of ΔaroA vaccine-strain and total E. coli load in ileal samples of vaccinated (n = 7) or non-vaccinated birds (n = 7).

Birds from the vaccinated group received 10⁸ CFU ΔaroA vaccine per bird at day of hatch. At 3 days of age (2 days after vaccination), ileal content was collected. (A) Simultaneous detection of the vaccine strain (targeting the mutant aroA gene) (dark grey bars) and total E. coli load (targeting the xanQ gene) (light grey bars) was obtained using the duplex qPCR. Total E. coli load in the ileum of vaccinated birds tended to be lower than in non-vaccinated birds (p = 0.053). (B) 92.4% of the total E. coli load in the vaccinated birds was attributed to the ΔaroA vaccine strain, whereas in the non-vaccinated birds, no vaccine strain was detected.