Cellulitis caused by Escherichia coli has been an increasing problem in Danish broiler production both in terms of welfare and economy. Different types of E. coli have previously been associated with cellulitis.
E. coli was isolated in pure culture from typical cellulitis lesions in 193 broilers representing 15 different flocks. In a number of cases, E. coli could also be isolated from the spleen and/or liver. Broilers examined were either dead on the farm or condemned at slaughter. E. coli isolates were investigated by Pulsed-Field-Gel-Electrophoresis (PFGE) for clonality, by Multi Locus Sequence Typing for comparison to sequence types (ST) in the database and Whole Genome Sequencing (WGS) to obtain knowledge about virulence genes.
All outbreaks investigated demonstrated clonality of E. coli. Different PFGE clones where found on different farms, but one clone was found to dominate causing cellulitis on 13 flocks. This clone was further investigated to determine which mechanisms that made this clone particularly fit to cause cellulitis. The clone belonged to ST 117, a ST which is well described as a pathogen in poultry in Europe, South-America and United States. WGS showed that the isolates representing this clone held from 20-22 virulence genes. Comparison of the virulence profile of the cellulitis isolates to other Avian-pathogenic E. coli originating from sepsis and salpingitis showed that the gene upaG was specific for the investigated strains. This gene encodes an autotransporter adhesion protein, and is described to be important in Uro-pathogenic E. coli for adherence to bladder epithelial cells. Further investigations will show, whether this gene plays an important role in the pathogenesis of cellulitis in broilers.