Pilot: Biotyping E. cecorum strains using a Chicken Embryo Lethality Assay

Abstract

Since 2002 there is an increase in incidence of Enterococcus cecorum lesions in chicken. Typical E. cecorum lesions are pericarditis, arthritis, osteomyelitis of the femur and 6th thoracic vertebrae and subsequently lead to clinical signs such as weakness, lameness, paralyses and a typical posture due to compression of the spinal cord. To investigate different strains of E. cecorum this pilot was performed to determine if an embryo lethality assay (ELA) is a suitable assay to determine if an E. cecorum is non-pathogenic or pathogenic. Various routes of inoculations were investigated to determine the success rates of inoculation and the route which can discriminate between the pathogenic and non-pathogenic E. cecorum strains. The E. cecorum ELA has been performed with allantoic cavity (AC), chorionallantoic membrane (CAM) and intravenous inoculation. The success rates of the amniotic, embryonic and yolk sac inoculation never reached a full score and therefore were not included. The ELA was performed on incubation day 10 and day 14 with 6 different E. cecorum strains and a control group. The AC inoculation resulted in a significant difference in survival between one pathogenic strain and the other inoculated strains, with the exception of the negative control strain. The CAM and IV inoculation resulted in a significant difference in survival between the inoculated pathogenic and non-pathogenic strain and the negative control ECE 3 strain. Based upon this pilot study, the CAM inoculation is currently the best inoculation route to discriminate between a pathogenic and a non-pathogenic E. cecorum strain in an embryo lethality assay. In addition, the AC inoculation route also provides evidence that it can be a reproducible and reliable method to discriminate E. cecorum strains.