Potential virulence genes of Haemophilus parasuis identified by differential display RT-PCR
Although 'Haemophilus parasuis' is an important bacterial pathogen of swine worldwide, little is known about its pathogenesis or why some strains seem more virulent than others. Therefore, differential display (DD) RT-PCR was used to identify virulence-associated genes in a pathogenic serotype 5 strain, 'H. parasuis' 1185. Gene expression was evaluated after growth in different conditions chosen to mimic those in the upper respiratory tract or during acute infection. Eight differentially expressed gene fragments were identified in cells grown at 40°C ± swine serum compared to 35°C and characterized. These included one with low homology to mammalian basement membrane-specific heparin sulfate proteins, two overlapping fragments with homology to many bacterial sodium and chloride-dependent ion transporters and another with homology to the AP4A hydrolase gene. Four other differentially expressed genes were detected which have homology to genes encoding proteins involved in different metabolic pathways. All the differentially expressed genes were present in all 15 'H. parasuis' reference serotypes.