Characterization of Escherichia coli and other bacteria isolated from condemned broilers at a Danish abattoir

Abstract

Meat inspection is important to ensure food safety and protect public health. Visual inspection of slaughtered carcasses for pathological changes should be supported by bacteriological analysis to determine whether the entire carcass or parts of it should be condemned. The aim of this study was to determine the bacterial species present in different sample types from condemned broiler carcasses. Furthermore, we investigated the genetic characteristics, zoonotic potential, and relatedness ofEscherichia coli, the predominant bacterial species isolated from the carcasses. A total of 400 broiler carcasses condemned because of cellulitis (100), scratches (100), hepatitis (100), and healthy control carcasses (100) were selected. Samples of meat, pathological lesion, and bone marrow of each carcass were obtained for microbial analysis. From the analyzed samples, 469 bacterial isolates were recovered withE.coliaccounting for 45.8%, followed byAeromonasspp. (27.9%), in particularA.veronii. The highest rate of bacterial isolation was observed in carcasses condemned with cellulitis, whereas carcasses with hepatitis had the lowest rate of bacterial isolation. Forty-fourE.coliisolates originating from different sample types were selected for whole genome sequencing. A clonal relationship was shown betweenE.colifrom different sample types of the same carcass condemned with cellulitis and scratches. A major clade ofE.coliwas found in carcasses condemned with cellulitis with isolates containingmdf(A),tet(A), andblaTEM-1Bgenes that confer resistance to macrolides, tetracycline, and ampicillin, respectively.E.coliin this clade all belonged to ST117 and clustered withE.coliisolates previously collected from dead chickens and carcasses condemned due to cellulitis in Denmark, Finland, and the United Kingdom. Bacterial evaluation results of carcasses condemned with cellulitis, scratches (moderate to severe skin lesion), and acute hepatitis confirmed the need for total condemnation of carcasses with these pathological findings. A similar evaluation should be done for carcasses affected with chronic hepatitis, and minor scratches lesions.