Characterization of Enterococcus faecalis Isolated from Pullet Layers with Growth Depression and Amyloid Arthropathy

Enterococcus faecalis is a commensal bacterium that colonizes the intestines of mammals and birds. It is characterized as an opportunistic pathogen and has been commonly associated with late-stage embryonic mortality, omphalitis, growth depression, sepsis, and amyloid arthropathy in poultry. In this study, E. faecalis isolates recovered from a flock of 6200 layer pullets located in Canada exhibited impaired growth, poor uniformity, and sporadic lameness that started at 1 wk of age and extended throughout the rearing phase. Enterococcus faecalis was isolated from swollen tarsometatarsal joints of lame pullets that contained yellow-orange material and from the house environment. Two sequence types (STs) known to be pathogenic to chickens, ST82 and ST49, were identified among the joint isolates. Seventeen known E. faecalis virulence genes were detected in these strains, including gelE for gelatinase production and the fsrB quorum-sensing signaling peptide gene required for virulence regulation. Phylogenetic analysis revealed that an ST82 strain isolated from an environmental sample was clonally related to the joint isolate. Furthermore, both sequence types, ST82 and ST49, had antimicrobial-resistance genes against tetracyclines, lincosamide, and streptogramin antimicrobials. ST49 had additional resistance genes to common ionophores used in poultry production. An embryo lethality assay was conducted to determine the pathogenicity of isolates. Inoculation with ST82 resulted in significantly lower survivability of embryos compared to ST49. To date, cases of amyloid arthropathy caused by E. faecalis are reported in European countries, but rarely from North American poultry operations. Further characterization of these E. faecalis strains is needed to elucidate transmission routes, uncover environmental reservoirs, and identify specific virulence genes in the development of amyloid arthropathy in poultry.