The characterisation and epidemiology of avian pathogenic Escherchia coli in UK broiler chickens

Poultry health and welfare are important for maintaining sustainable and safe food production. In the UK alone, in excess of 900 million broiler chickens are farmed annually with demand continuously increasing. Avian pathogenic Escherichia coli (APEC) is the causative agent of the extraintestinal syndromic poultry disease colibacillosis, which has a major impact on poultry health and is a considerable economic burden to the global poultry industry. The need for disease control is of paramount importance. Little is known about the epidemiology, population dynamics and infection biology of APEC in UK broiler chickens. This knowledge would contribute to the implementation of control measures. This investigation comprised: one longitudinal field study in commercial flocks aimed at simultaneously identifying potential APEC (pAPEC) in the intestinal tract of healthy birds and extraintestinal E. coli in diseased birds, one study determining the contribution of E. coli to early flock mortalities and a series of in vitro experiments and genetic analyses characterising both extraintestinal and avian faecal E. coli isolated from UK broiler chickens. E. coli were subjected to virulotyping, phylogenetic typing, macro-restriction pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). The extraintestinal E. coli isolates from diseased birds represent a diverse genetic population. Furthermore, as broiler chickens age, the prevalence of pAPEC in the gastrointestinal tract decreases. The intestinal tract of day-old chicks contains considerable levels of pAPEC (24.05% of the faecal population sampled), while ~70% of early mortalities relate to extraintestinal E. coli infections, possibly originating from the gut. In vitro, pAPEC did not appear to invade intestinal epithelial cells, suggesting the respiratory route is likely to be favourable for dissemination, although pAPEC are cytotoxic and may disrupt epithelial integrity prior to dissemination. There were no significant differences in the intracellular persistence of APEC and faecal E. coli in cultured avian macrophages and survival in serum; challenges encountered by E. coli during dissemination. Overall, this investigation highlights the diverse spectrum of E. coli associated with extraintestinal disease in commercial broiler production and the need to determine the contribution of host susceptibility to disease manifestation