A Pilot Study of Enterococcus cecorum as a Potential Etiological Agent of Broiler Chicken Disease in Bulgaria

An outbreak of early-onset disease associated with Enterococcus cecorum was investigated in two commercial Ross 308 broiler flocks in southern Bulgaria in November 2025. Clinical signs developed at approximately 20 days of age and included lameness, recumbency and impaired mobility. Reported flock mortality was 2.8% and 3.7% in the respective flocks. Nineteen dead birds were submitted, of which 13 (four from Farm A and nine from Farm B) were suitable for diagnostic examination. Necropsy and histopathology revealed systemic and osteoarticular lesions, including fibrinous pericarditis, perihepatitis, cartilage erosion, osteomyelitis and spondylitis. A total of 62 anatomical-site cultures were examined independently; 42/62 (67.7%) yielded E. cecorum, and pure growth was recorded in 11/13 examined birds (84.6%). Five selected isolates underwent molecular characterization, including sodA-based species confirmation and screening for cpsO and selected virulence-, antimicrobial-resistance- and conjugation-associated genes. Detection of these markers indicates genetic potential but does not establish their expression, phenotypic resistance or primary causation. Because validated species-specific clinical breakpoints were unavailable for the disk-diffusion conditions used, inhibition zones were reported descriptively. The observations support an association between systemic E. cecorum infection and disease in the investigated birds, warranting larger, controlled investigations.