Abstract Haemophilus parasuis is a kind of symbiotic bacteria in upper respiratory tract of pigs, but it can invade the body and cause serious systemic disease under certain conditions. Distinction between virulent strains and avirulent strains is the key point for diagnose of the disease. In order to search for differentially expressed proteins between virulent and attenuated strains of H. parasuis, the proteomics of the cytosolic proteins were compared between H. parasuis virulent 14A7-2 strain and avirulent 20A3-2 strain by two-dimensional gel electrophoresis. The cytosolic proteins of two strains were extracted at late logarithmic phase for 2-DE. After electrophoresis, the gels were analyzed with Imagemaster 2D Platinum 7.0 software, and differentially expressed proteins were identified by MALDI-TOF/MS. By 2-DE and analysis, the results showed that there were 586±10 protein spots in virulent strain and 568±10 in avirulent strain. A total of 80 protein spots were differentially expressed in the two strains. 44 protein spots unique for 14A7-2 or 20A3-2 strain were selected to be identified by mass spectrometry, and 42 protein spots were successfully identified corresponding to 37 proteins. Five proteins were unique for non-virulent strain, while 27 proteins were unique for virulence strains which included ferric uptake regulation protein, trigger factor and 3-dehydroquinate dehydratase associated with virulence. These results provide new information for further studies of virulent factors, pathogenic mechanisms and diagnostic techniques to distinguish different virulence strains of H. parasuis.
