Bacterial chondronecrosis with osteomyelitis related Enterococcus cecorum isolates are genetically distinct from the commensal population and are more virulent in an embryo mortality model

Abstract

Bacterial chondronecrosis with osteomyelitis (BCO) is a common cause of broiler lameness. Bacteria that are found in BCO lesions are intestinal bacteria that are proposed to have translocated through the intestinal epithelium and have spread systemically. One of the specific bacterial species frequently isolated in BCO cases is Enterococcus cecorum. In the current study, caecal isolates were obtained from birds derived from healthy flocks (12 isolates from 6 flocks), while isolates derived from caeca, colon, pericardium, caudal thoracic vertebrae, coxo-femoral joint, knee joint and intertarsal joint (hock) were obtained from broilers derived from BCO outbreaks (111 isolates from 10 flocks). Pulsed field gel electrophoresis was performed to determine similarity. Clonal E. cecorum populations were isolated from different bones/joints and pericardium from animals within the same flock, with intestinal strains carrying the same pulsotype, pointing to the intestinal origin of the systemically present bacteria. Isolates from the intestinal tract of birds from healthy flocks clustered away from the BCO strains. Isolates from the gut, bones/joints and pericardium of affected animals contained a set of genes that were absent in isolates from the gut of healthy animals, such as genes encoding for enterococcal polysaccharide antigens (epa genes), cell wall structural components and nutrient transporters. Isolates derived from the affected birds induced a significant higher mortality in the embryo mortality model as compared to the isolates from the gut of healthy birds, pointing to an increased virulence.

Molecular Genomic Analyses of Enterococcus cecorum from Sepsis Outbreaks in Broilers

“…We interpret all of the phylogenomic data as most consistent with pathogenic isolates arising from non-pathogenic isolates and that sepsis isolates are closely related to BCO isolates. Our conclusions contrast with those from previous analyses of smaller collections of genomes that suggested distinct lineages for commensal and pathogenic isolates of E. cecorum [ 13 , 16 , 37 ].…”

Characterizing the impact of Enterococcus cecorum infection during late embryogenesis on disease progression, cecal microbiome composition, and early performance in broiler chickens

“…Phenotypic and genotypic analyses have been used to categorize and differentiate between commensal and pathogenic strains of EC ( Borst et al, 2015 ; Dolka et al, 2016 ; Borst et al, 2017 ; Jung et al, 2017 ). Virulence of EC strains has also been assessed in vivo with embryo lethality assays ( Borst et al, 2014 ; Jung et al, 2017 ; Ekeski et al, 2021 ; Dolka et al, 2022 ; Manders et al, 2022 ; Huang et al, 2023 ). Schreier et al (2021) demonstrated that an EC isolate that caused high embryonic mortality, and deemed to be pathogenic, did not induce disease when administered to chicks at hatch.…”