In situ hybridisation in endometrial biopsies of horses: a diagnostic approach to bacterially induced endometritis?

Abstract

While in human medicine bacterial biofilms are recognized as a common cause of persistant and relapsing infections, little is known about their existance in the genital tract of the mare. A broad variety of organisms, however, are known as etiologic agents for equine endometritis. In this context, the use of in situ hybridisation (ISH) as a diagnostic tool was assessed. Endometrial biopsies were obtained from 395 thoroughbred mares with fertility disturbances and bacterial genital infections with Streptococcus spp. (96 mares), E. coli (99 mares), Pseudomonas spp. (21 mares), and Klebsiella spp. (7 mares). Bacteria were detected by cultural examination of uterine swabs. The biopsies were processed for conventional H.-E.-staining and for in situ hybridisation (ISH) with Digoxigenin-labelled probes. Histologically, 30 mares with streptococcal infection showed an endometritis varying in degree and character. By means of ISH Streptococcus spp. were detected in the endometrium of 14 horses, including 6 with endometritis and 8 without an inflammation of the uterus. The bacteria were located on the luminal epithelium and in the superficial secretory ducts of the uterine glands. From the 99 mares with E. coli infections, 36 animals suffered from an endometritis, and in 4 biopsies without inflammatory reactions DNA of E. coli could be labelled. The detection of Klebsiella spp. and Pseudomonas spp. using ISH was not possible. Although cultural examination of uterine swabs provides more comprehensive results, by means of ISH the spatial organisation of bacteria in the endometrium can be characterised. In this study no evidence for the formation of biofilms by Streptococcus spp. or E. coli was found, but nevertheless they may possibly contribute to endometritis in some cases.