Genetic Comparison of Enterococcus Species Isolated from Osteomyelitis Lesions and the Barn Environment of Successive Broiler Chicken Flocks.

Osteomyelitis caused by Enterococcus cecorum is an emerging disease in broiler chickens in Canada. Other Enterococcus species have been reported as causative agents in certain outbreaks. The epidemiology of this disease is unknown, but contaminated barns are affected by recurring episodes. A broiler chicken flock located in Quebec, Canada, exhibited osteomyelitis lesions positive for E. cecorum and Enterococcus faecalis. Surprisingly, the following lot, in the same barn, revealed the presence of E. faecalis- and Enterococcus raffinosus-positive lesions but no E. cecorum. To better understand the epidemiology of these two outbreaks, verify the persistence of pathogenic isolates in the barn, and identify the possible transfer of genetic material between the Enterococcus species isolated from both events, 16 isolates (1 E. cecorum, 13 E. faecalis, and 2 E. raffinosus isolates) were sequenced, and their genomes were compared. Interestingly, more than one Enterococcus species could be isolated from the same lesion, while other lesions also revealed several nonclonal isolates from the same species. This might suggest the opportunistic nature of Enterococcus spp. as there was no predominant isolate in the lesions. The number of virulence genes varied from 1 to 34 across three Enterococcus species with no common virulence gene. The number and nature of antimicrobial resistance genes among those isolates were worrisome because they indicate the presence of multidrug resistance on the farm. Both plasmids and phages were shared by different Enterococcus species, which suggests potential horizontal gene transfer of mobile genetic elements within this enterococci population.