Entercoccus cecorum: an emerging infection of chickens in North America

About 4-5 years ago there was an increase in the number of chickens in Ontario that were affected by conditions such as arthritis and osteomyelitis (inflammation in the bone marrow). It was discovered that a bacterium called Enterococcus cecorum was the culprit. Such infections with E. cecorum were known from other places in the world, but had remained infrequent in North America. The sudden occurrence of disease outbreaks sparked an interest in the research community. Through collaborations between Dr Boerlin from the Department of Pathobiology, University of Guelph and the Animal Health Laboratory, some very interesting results have been obtained. Dr Boerlin and fellow researchers were able to compare the E. cecorum bacteria that were present in clinical specimens and those present in the gut of healthy chickens. The result suggested that the disease causing E. cecorum bacteria were very similar to one another, but different from those isolated from healthy birds.

It is not clear how or why a benign and harmless inhabitant of the gut could change its profile and cause disease. But since a similar pattern has been observed earlier in Europe, the disease causing strain in Ontario could possibly have originated from abroad. Dr Boerlin suggests that this study is important for determining the direction of further research. Comparative genomics (a look at structure and function of the whole genome using DNA sequencing and bioinformatics) is being taken up to compare in more details the differences between the strain identified in clinical cases and the commensal organisms that are found in healthy chickens. This could also determine how the strain came about and used to identify markers that distinguish between the disease causing strain and the harmless ones.

Dr Boerlin suggests this is important for the poultry industry as “it tells them that it is the spread of a particular strain which is responsible for disease outbreaks and perhaps not so much some change in management practices that has provoked the appearance of the disease.” Also the end result of the comparative genomics could give answers as to whether the virulence factors (i.e. the factors associated with the ability of the microorganism to cause disease) are easily transferable between bacterial strains through mobile genetic elements or not. If the former is true, there is a potential for the emergence and spread of further virulent strains in the future. Furthermore, from the perspective of the industry the research conducted by Dr Boerlin and colleagues helps determine susceptibility of virulent E. cecorum to antibiotics and may assist in identifying specific targets for intervention and developing novel vaccines against the disease.