Taylorella equigenitalis is a Gram-negative, non-motile, microaerophilic bacterium of the genus Taylorella, and the causative agent of contagious equine metritis (CEM) in horses. Phylogeny of T. equigenitalis includes being part of the Alcaligenaceae family.
Taylorella equigenitalis's distribution and habitat are primarily in the urethral fossa, distal urethra, prepuce, free-part of the penis of stallions and the clitoral fossa or sinus of mares. Canada and the USA are T. equigenitalis free, compared to other countries like those in Europe. Infected stallions are asymptomatic and act as the principal source of infection for mares during mating, and their carrier status may persist for many months or even years. A mare that becomes infected normally has recognizable signs unless asymptomatic, contributing to the spread of disease. A symptomatic mare can be identified by the mucus and pus being expelled from her vagina; CEM mares experience an inflamed endometrium causing low fertility and if pregnant a high probability for abortion in the first trimester.
Diagnosis, treatment and prevention of the disease are crucial to managing T. equigenitalis. Diagnosis is best done on chocolate agar or by polymerase chain reaction (PCR) with a sample from the urethral or clitoral fossa. Treatment includes disinfecting the external genital areas with 4% chlorhexidine as well as starting an antibiotic such as ampicillin. Prevention involves testing of new horses brought into the breeding herd, as well as isolation of horses entering T. equigenitalis free countries. Taylorella equigenitalis can have detrimental effects on the equine industry both clinically and economically due to the infertility it causes and the impact on import and export of equine genetics.
Phylogeny
The first identification of Taylorella equigenitalis was by Taylor et al., in 1978 and was referred to at the time as Haemophilus equigenitalis. Due to specific genomic characteristics and DNA hybridization results, Sugimoto et al., proposed the change from Haemophilus genus to Taylorella in 1983. There are two identified species of Taylorella equigenitalis, one of which is resistant to streptomycin. Taylorella equigenitalis is an infectious organism for horses and Taylorella asinigenitalis has been isolated from the genital tracts of male donkeys. Gross morphology and growth rates of T. equigenitalis and T. asinigenitalis are too similar to differentiate the two species without the use of molecular identification techniques such as PCR. Molecular evaluation of the 16S rDNA sequence has confirmed that there is enough of a genetic difference between Taylorella equigenitalis and Taylorella asinigenitalis to separately classify the two species. Taylorella asinigenitalis does not appear to cause disease in equine mares, only in donkeys. Taylorella equigenitalis was previously identified as belonging to the Pasteurellacae family. It is now classified as belonging to the Alcaligenaceae family.
Morphology
Taylorella equigenitalis is a Gram-negative bacterium, which grows best under specific environmental conditions on the reproductive organs, and in the reproductive tract of horses. Taylorella equigenitalis is morphologically identified as coccobacillary or bacillus. Members of the genus Taylorella including T. equigenitalis are non-motile and microaerophilic. Herbert et al., have reported that T. equigenitalis have a capsule and express pili in vivo. Taylorella equigenitalis is pleomorphic on isolation from equine carriers, and there is no formation of endospores. Taylorella equigenitalis has scant growth on blood agar, the best growth is observed on chocolate agar at temperatures between 30 and 42 degrees Celsius. Taylorella equigenitalis tests positive on oxidase, catalase, phosphatase and phosphoamidase reactions and negatively on glucosidase, indole, hydrogen sulfide and production of chemoorganotrophic acid from carbohydrates. T. equigenitalis is sensitive to penicillin type antibiotics.