A French research team sequenced the genome of Taylorella equigenitalis, the causative agent of the equine venereal disease contagious equine metritis (CEM), as well as T. asinigenitalis, a closely related species generally isolated in donkeys.

The Taylorella organism is difficult to grow in culture and, therefore, difficult to study outside the host animal's body. Previous studies of its structure and behavior show that it can invade the reproductive tract's mucosal layer and infect mares' uterus, cervix, and vagina, although the precise process of infection is unknown.

Using next-generation sequencing technologies and bioinformatics analysis, the research team compared both species' gene sequences with the following results:

• About 80% of genes are common to both species, and the order of the genes is similar; this indicates that the two are closely related and that each is well adapted to its ecological niche;

• Both species' metabolic genes are consistent with clinical observations that the bacterium cannot survive well outside a host, so it is likely that infections are from other animals, not bacteria in the environment;

• Both species have genes that code for proteins and mechanisms that work by attaching to and invading the reproductive system's mucosal tissues. Protein secretion is a key virulence mechanism of bacteria, according to the authors;

• T. equigenitalis (the bacterium that mainly infects the horse) seems better equipped to infect, possessing more protein secretion genes; and

• Genes associated with tissue destruction are absent in Taylorella, which could explain why it stays in the reproductive system and does not invade or damage host tissues.

The next step, according to Laurent Hébert, PhD, research associate of the Dozulé Laboratory for Equine Diseases at the French Agency for Food, Environmental, and Occupational Health and Safety, is to develop tools to link specific genes to different mechanisms of infection in order to provide information about how the bacterium infects the horse, with a view toward developing future therapies