Detection and localization of ApxI, -II, and -III genes of Actinobacillus pleuropneumoniae in natural porcine pleuropneumonia by in situ hybridization

In situ hybridization techniques that employed a nonradioactive digoxigenin -labeled probe were used to detect and localize ApxI, II and III genes in t issue sections of pneumonic lung naturally infected with Actinobacillus ple uropneumoniae. In pigs infected with either serotype 2 or 6, a hybridizatio n signal for apxIICA, apxIIICA, npxIBD, and apxIIIBD was detected, and in p igs infected with serotype 5, a hybridization signal for apxICA, apxIICA, a nd apxIBD was detected in the pneumonic lesions. A hybridization signal for npxIICA and apxIBD was detected in pigs infected with serotype 7. A strong hybridization signal for apx genes was seen in streaming degenerate alveol ar leukocytes bordering zones of coagulative necrosis. Simultaneous detecti on of hybridization signals for the apxCA and apxBD genes provided scientif ic evidence that the expression of the apx genes could be potential indicat ors of the production of corresponding Apr toxins. This study demonstrates the expression of ApxI, II, and III genes in pneumonic lesions caused by A. pleuropneumoniae.