Detection of Streptococcus suis by in situ hybridization, indirect immunofluorescence, and peroxidase-antiperoxidase assays in formalin-fixed, paraffin-embedded tissue sections from pigs

Streptococcus suis is an important pathogen in pigs and is considered a zoo notic agent. To aid diagnosis of infection caused by S. suis, a species-spe cific probe targeting 16S ribosomal RNA was designed and used for fluoresce nt in situ hybridization. Two additional immunohistochemical detection meth ods, an indirect immunofluorescence assay and a peroxidase-antiperoxidase m ethod, using polyclonal antibodies also were developed. The specificity of the oligonucleotide probe was examined by whole-cell and dot-blot hybridiza tion against reference strains of the 35 serotypes of S. suis and other clo sely related streptococci and other bacteria commonly isolated from pigs. T he probe was specific for S, suis serotypes 1-31. The specificity of the po lyclonal antibodies, which has previously been evaluated for use in diagnos tic bacteriology for typing of serotype 2, was further evaluated in experim entally infected murine tissue with pure culture of different serotypes of S. suis, related streptococci, and other bacteria commonly found in pigs. T he polyclonal antibodies against S. suis serotype 2 cross-reacted with sero types 1 and 1/2 in these assays. The in situ hybridization and the immunohi stochemical methods were used for detection of S. suis in formalin-fixed, p araffin-embedded tissue sections of brain, endocardium, and lung from pigs infected with S. suis. The methods developed were able to detect single cel ls of S. suis in situ in the respective samples, whereas no signal was obse rved from control tissue sections that contained organisms other than S. su is. These techniques are suitable for determining the in vivo localization of S. suis for research and diagnostic purposes.