An enzyme-based in situ hybridisation method for the identification of Streptococcus suis - Brief report

A method for enzyme-based in situ hybridisation of Streptococcus suis was d eveloped. It enables the light microscopic localization of bacterial riboso mal RNA (rRNA) in formalin-fixed paraffin-embedded tissues. A unique sequen ce in the 16S rRNA of S. suis was targeted. Different pretreatment protocol s were applied to facilitate probe penetration and multiple detection syste ms were tested. The results were compared to those obtained by immunohistoc hemistry. Pretreatment was necessary to obtain a signal by in situ hybridis ation. The use of proteinase-K pretreatment was optimal regarding sensitivi ty and preservation of tissue morphology. A strong specific in situ hybridi sation signal was achieved in tissue sections containing S. suis in microco lonies and the microanatomy of the surrounding tissue was easily assessed. However, the signal distribution differed from that found immunohistochemic ally and low-grade infection could not be detected by in situ hybridisation . These findings were interpreted as reflecting the physiological state of the bacteria. Thus, this method could prove useful in future studies of the infection pathogenesis.