Enterococcus cecorum is a normal inhabitant of the intestine and a cause of arthritis and osteomyelitis in chickens. It has recently emerged as a new pathogen in Canada. Little is known about its diversity and the relationships between clinical isolates and those from the normal gut flora.

The objectives of the study were to collect E. cecorum isolates from chickens in Ontario; to develop and apply a molecular typing method (PFGE) to assess relationships between E. cecorum isolates; to assess the susceptibility of E. cecorum isolates to antimicrobial agents.

E. cecorum isolates were recovered from 28 clinical infections in 24 farms and from the ceca of 34 healthy birds from 23 farms. Isolates were identified using biochemical tests and genetic methods (16S rRNA gene sequencing). A new PFGE protocol was developed to type E. cecorum, which was used to compare the 62 isolates from our collection.

The results show that a large diversity of E. cecorum strains are present in the gut of healthy birds but that most E. cecorum isolates from lesions in sick birds are similar to one another. This strongly supports the hypothesis that one particular E. cecorum strain has emerged recently in Ontario and is responsible for the majority of recent infections and outbreaks.

Antimicrobial susceptibility testing showed widespread and very frequent resistance to erythromycin, streptomycin, tetracycline and bacitracin in E. cecorum in general, but not to penicillin. The isolates responsible for clinical infections are more frequently resistant to erythromycin, tylosin and streptomycin than those from the gut of healthy birds. Similar but less obvious trends were observed for enrofloxacin, florfenicol, neomycin and gentamicin. However, isolates from healthy birds were more frequently resistant to clindamycin in vitro.

This study provides a strong basis for detailed comparisons between representative isolates from clinical infections and from the gut of healthy birds in order to identify the characteristics which make some E. cecorum more prone to cause infections and outbreaks than others. Such comparisons may help develop more efficient therapies and vaccines for the prevention of E. cecorum infections.

January 2011