1. F A C U L T Y O F L I F E S C I E N C E S U N I V E R S I T Y O F C O P E N H A G E N Genetic diversity of S. equi subsp. zooepidemicus and E. coli isolated from the reproductive tract of the mare Mette M. Bindslev, Maria H. Villumsen, Morten M. Petersen, Jesper M. Nielsen, Ingrid B. Bøgh, Anders M. Bojesen Departments of Veterinary Patobiology and Large Animals Sciences Aims The aim of this study was to evaluate the genetic diversity between isolates of S. equi ssp. zooepidemicus and E. coli isolated from the fossa clitoridis, vagina and the uterus of mares. Furthermore, the study aimed at evaluating a possible correlation between the presence of polymorphnucleated neutrophils (PMN’s) in the endometrium and infection with S. equi ssp. zooepidemicus or E. coli. Materials & Methods A total of 89 mares were included in this study. The samples were collected from two groups of mares; one group of individual mares with no epidemiological relationship and one group of mares (21) from a closed herd. Swabs from clitoris and the vagina and an endometrial biopsy from the uterus were examined for growth of E. coli and S. equi ssp. zooepidemicus. Up to three isolates of each bacterial species from either anatomical site were investigated. In addition, cytological smears from uterine biopsies were evaluated for the presence of PMN’s. A sample was considered positive when more than 0.5 % of all cells in the sample were PMN´s. Fossa clitoridis Three isolates selected Uterus Three isolates selected Uterus Three isolates selected Vagina Three isolates selected 89 mares Bacterial culture from fossa clitoridis, vagina and uterus Enumeration of PMN’s in the endometrial mucosa If present, three isolates of S. zooepidemicus and E. coli from fossa clitoris, vagina and uterus, respectively, are kept Purification of bacterial DNA and evaluation of the genetic diversity of 90 S. zooepidemicus and 217 E. coli isolates by Amplified Fragment Lenght Polymorphism Test of hypothesis: ”Endometritis is caused by a specific endometritis-type of S. zooepidemicus and E. coli, different from the resident flora” Results The genetic diversity of the isolated E. coli and S. equi ssp. zooepidemicus was determined by Amplified Fragment Length polymorphism. Out of 213 E. coli isolates, 127 different fragment profiles were identified, whereas 54 profiles were recorded among the 90 S. equi ssp. zooepidemicus isolates investigated, indicating a high genetic diversity among the isolates. Endometritis caused by S. equi ssp. zooepidemicus was often caused by more than one bacterial clone (64% of the cases), whereas this was a more rare in infections caused by E. coli (36%). Finally, we observed no difference in the genetic diversity among S. equi ssp. zooepidemicus or E. coli isolated from clitoris of mares from the confined herd when compared to isolates from mares kept as on an individual basis. Furthermore, positive cytology is a not a reliable tool to evaluate the infectious status as presence of PMN’s was absent in 33% or 67% of infections caused by S. equi ssp. zooepidemicus or E. coli, respectively. Conclusions We did not find support for the hypothesis, stating that endometritis is caused by a specifc ”endometritis- type” of either S. zooepidemicus or E. coli. On the contrary, it appeared that for both bacteria, clones involved in endometritis were part of the normal reproductive tract flora. Furthermore, more than one bacterial clone were often present in the same anatomical location. Although based on a small data material, it appeared that E. coli often could be isolated without having elicited an immunological response including PMN’s. Perspectives Specific bacterial factors promoting endometritis, possibly tranmissible among unrelated bacterial clones, should be searched for. The abillity to cause immunologically ”silent” infections should be documented and characterized in further detail. The fact that often multiple clones of the same species is present during endometritis warrents more thorough investigation of i.e. antibiotic resistance at treatment