Differences between Taylorella equigenitalis strains in their invasion of and replication in cultured cells

The ability of Taylorella equigenitalis, the causative agent of contagious equine metritis, to invade and replicate in equine derm cells was studied. The kinetics of invasion and replication were determined for four T. equigenitalis strains. On the basis of these experiments, a simpler assay in which the invasive as well as the replicative properties of a particular strain could be determined was developed. This assay was used to characterize 32 strains, which had previously been typed by field inversion gel electrophoresis of genomic restriction fragments. The invasiveness of T. equigenitalis strains ranged from 3 to 0.015 bacteria per cell and seemed to be associated with the contagiousness of the infection. The replication index (number of intracellular bacteria per cell at 24 h after inoculation divided by the number of intracellular bacteria per cell at 4 h after inoculation) varied from 1 to 857 and seemed to be associated with the severity of the symptoms of contagious equine metritis. There was no association between the invasiveness and the replication index of the strains, nor was there an association of invasion and replication with field inversion gel electrophoresis grouping.