Development of in-situ hybridization for the detection of Mycoplasma haemosuis (Eperythrozoon suis) in formalin-fixed, paraffin wax-embedded tissues from experimentally infected splenectomized pigs

Mycoplasma haemosuis DNA was detected in experimentally infected splenectomized pigs by in-situ hybridization (ISH) with a nonradioactive digoxigenin-labelled DNA probe. An 839 base pair DNA probe targeting a 16S rRNA gene was generated by the polymerase chain reaction. Eight 6-week-old pigs were inoculated intraperitoneally with 6 ml of M. haemosuis-infected pig blood and eight negative control pigs were inoculated intraperitoneally with 6 ml of M. haemosuis-free blood. Two pigs from each group were killed for examination at 3, 7, 15 and 30 days post-inoculation (dpi). Red blood cells infected with M. haemosuis were first detected by light microscopy at 3 to 7 dpi. No M. haemosuis was observed in negative control pigs. Hybridization signals were evident in blood from the infected pigs at 3 dpi. The ISH method developed in this study was useful for the detection of M. haemosuis DNA in formalin-fixed, paraffin wax-embedded tissues and may be valuable for studying the pathogenesis of M. haemosuis infection.