FIG. 4.

Role of the aec-35-aec-37 gene cluster in the colonization of liver and blood and in the development of colibacillosis lesions in chickens. Twenty and 19 25-day-old specific-pathogen-free White Leghorn chickens were inoculated in the right air sac with 5 × 10⁶ CFU of strains BEN2908 or BEN2929, respectively. Three chickens were inoculated with the nonpathogenic avian strain BEN2269. Each animal is represented by a diamond symbol (⧫, ⋄). Bacteremia was determined 24 h (A) and 48 h (B) postinoculation. Animals were euthanized 48 h postinoculation by injection of Nesdonal and then necropsied. Liver bacterial colonization (C) and colibacillosis lesions (D) were recorded. The lesion score was not determined for dead animals. In each group infected by either BEN2908 or BEN2929, four chickens died and were given the highest rank. They are represented by an open diamond symbol (⋄). Bars indicate the median for each group of chickens. A Wilcoxon-Mann-Whitney test was used to analyze the differences between groups of chickens inoculated with the wild-type and the mutant strains (*, P < 0.05; **, P < 0.01).