Subcutaneous inoculation of Escherichia coli in broiler chickens causes cellulitis and elicits innate and specific immune responses

Coliform cellulitis is a common cause of condemnation of broiler chickens at slaughter worldwide, and is associated with economic losses and possible negative impact on welfare. The study objective was to monitor clinical signs and immune response after subcutaneous E. coli inoculation (1.1–1.8*107 CFU), aiming to induce cellulitis. Three groups of broiler chickens (n=15/group) were inoculated with one of two well-characterized E. coli strains (groups A and B) or with saline (control) at 22 days-of-age. Clinical signs of disease, body weight and immune parameters were monitored. Chickens were euthanized 12–14 days after inoculation followed by post-mortem examination. The daily weight gain was significantly reduced one day after inoculation compared to controls, but few chickens displayed clinical signs. A transient increase of chicken mannose receptor MRC1L-B expression on circulating monocytes was observed one day after inoculation in groups A and B. On day 7 after inoculation, the in vitro adherence of heterophils, monocytes and thrombocytes to the inoculated strain was increased in group B. Antibody titers to the inoculation strains were increased in some chickens in both groups on days 7 and 14 after inoculation. Seven (47%) and 13 (87%) of the chickens in group A and B, respectively, were diagnosed with cellulitis at post-mortem examination. In most birds, lesions consisted of plaque-like material enclosed either in subcutaneous tissue or within the abdominal wall. In conclusion, inoculation of E.coli caused cellulitis and prompted a rapid activation/redistribution of circulating monocytes followed by antibody production.