In situ hybridization for the detection and localization of swine Chlamydia trachomatis

Gnotobiotic piglets were inoculated intralaryngeally with swine Chlamydia t rachomatis strain R33 or orally with swine C. trachmatis strain R27. Archiv ed formalin-fixed, paraffin-embedded tissues from piglets euthanatized 4-7 days postinoculation were examined by in situ hybridization for C; trachoma tis nucleic acid using a nonradioactive digoxigenin-labeled DNA probes that targeted specific ribosomal RNA or omp1 mRNA molecules of the swine C. tra chomatis strains. Positive hybridization signals were detected in bronchial epithelial cells, bronchiolar epithelial cells, pneumocytes, alveolar and interstitial macrophages, and jejunal and ileal enterocytes. Chlamydia-infe cted cells had a strong signal that was confined to the intracytoplasmic in clusions. Positive hybridization signals were not detected in tissue sectio ns from an uninfected control piglet or in C. psittaci-infected sheep place nta. The morphology of host cells was preserved despite the relatively high temperature required in parts of the incubation procedure. The data indica te that in situ hybridization can be used to detect swine C. trachomatis in formalin-fixed, paraffin-embedded tissue specimens.