Research Note: Comparison of Enterococcus cecorum genomes from broiler chickens with enterococcal spondylitis in Australian farms and strains from other countries.

Chickens in Australia have recently been identified with symptoms and morphological findings including spondylitis attributed to pathogenic Enterococcus cecorum. Notably, there is limited information on clinical E. cecorum strains in Australia. The cpsO gene, located downstream of the capsular polysaccharide (cps) locus, was recently reported to successfully differentiate between pathogenic and commensal E. cecorum strains, as this gene is highly conserved in the pathogenic strains. In this study, pathogenic E. cecorum, with a conserved cpsO gene, was detected on 1 of the 2 farms studied in Australia. E. cecorum strains isolated from clinical sites of the diseased birds from the second farm did not have the cpsO gene and were distant from the isolates of the first farm. A cpsO PCR of the caecal content of the birds on this farm was positive, while cpsO PCR of washed culture plates where the tissue extracts were spread onto and incubated for bacterial growth was negative. This suggests that pathogenic E. cecorum with the cpsO gene, as detected in Farm 1 and reported in other countries, was present in the second farm but could not grow on the selective agar plates during the initial step of E. cecorum isolation. Nevertheless, E. cecorum isolated from the clinical sites on the second farm might represent the pathogenic strain, but further animal studies are required to validate this possibility. Phylogenetic analysis showed that the pathogenic strains in Australia were most closely related to the clinical strains in North America.