Fig. 3

Chickens with dysbiosis are more susceptible to systemic avian pathogenic Escherichia coli (APEC) infection and changes in immune cell composition. A Chickens (n = 6 per group) were infected with APEC 3 d prior to florfenicol treatment and then re-infected following the withdrawal phase. B and C Body weight changes (B) and pathobionts in the cecal contents (C) were examined 3 dpi by plating the cecal contents on MacConkey agar plates. D Systemic APEC infection was quantified by determining the mean log₁₀ CFU/mL in a splenic suspension plated on MacConkey agar plates. E The serotype of the APEC colonies was identified by comparing antigen transcripts (wzx and neuC1). APEC and E. coli K88 from stock cultures served as positive and negative controls, respectively. F–G Changes in the percentage and absolute numbers of splenic monocytes/macrophages and lamina propria γδ T cells were determined. The frequency of monocytes/macrophages was expressed as a percentage of the total CD45⁺ population, whereas the frequency of γδ T cells was expressed as a percentage of the CD45⁺CD3⁺ population. NT, non-treated. T.T, APEC double infection without florfenicol treatment. T.F.T, APEC double infection with florfenicol treatment. Significance differences were examined by using Tukey test, with significance levels denoted as follow: *P < 0.05, **P < 0.01, ***P < 0.001