PCR detection of Actinobacillus pleuropneumoniae apxIV gene in formalin-fixed, paraffin-embedded lung tissues and comparison with in situ hybridization

Aims: Formalin-fixed, paraffin-embedded lung tissues from pigs experimentally infected with 12 Actinobacillus pleuropneumoniae serotypes were used to develop nested PCR for the detection of apx IV gene. Methods and Results: The PCR results from formalin-fixed, paraffin-embedded tissues were compared with in situ hybridization. The apx IV gene was detected in formalin-fixed, paraffin-embedded lung tissues from all 39 pigs experimentally infected with 12 A. pleuropneumoniae serotypes by nested PCR. In situ hybridization produced a distinct positive signal in all 39 pigs experimentally infected with 12 A. pleuropneumoniae serotypes. Agreement rates between nested PCR and in situ hybridization were 100% for the detection of apx IV gene in formalin-fixed paraffin-embedded lung tissues. Acceptable PCR signals were detected from lung tissues fixed for periods up to 180 days. Conclusions: The apx IV gene is species-specific rather than serotype-specific and is therefore an important diagnostic marker. The nested PCR assay would be a useful method for the detection of apx IV gene to diagnose A. pleuropneumoniae infection when formalin-fixed tissues are submitted. Significance and Impact of the Study: This study confirmed the possibility of using formalin-fixed, paraffin-embedded tissues for the diagnosis of A. pleuropneumoniae infection in pigs.