Outer membrane proteins and DNA profiles in strains of Haemophilus parasuis recovered from systemic and respiratory sites

Polyserositis caused by Haemophilus parasuis is an important disease that a ffects mostly weaned pigs. Recent studies have shown that virulence can dif fer among strains recovered from distinct body sites and also that it may b e related to the presence of certain outer membrane proteins (OMPs). The ob jective of this study was to compare the OMP and DNA profiles of H. parasui s strains isolated from systemic and respiratory sites from diseased and he althy pigs. Strains evaluated in this study were processed using sodium dod ecyl sulfate-polyacrylamide gel electrophoresis and repetitive-PCR techniqu es. Two experiments were conducted in order to better define the relationsh ip among genotype, phenotype, and site of isolation. Experiment 1 included 53 H. parasuis isolates recovered from healthy and diseased pigs from unrel ated herds. Experiment 2 included 31 isolates of H. parasuis obtained from diseased pigs involved in an outbreak in a large, multifarm system. Results showed that strains recovered from systemic sites had more homogeneous OMP and DNA profiles than those isolated from respiratory sites. Evaluation of isolates involved in the multifarm outbreak showed that only two H. parasu is strains were causing disease. These strains had homogeneous OMP and DNA profiles. However, it was noted that these two parameters were unrelated, s ince strains classified in the same genotype group expressed different OMP profiles. The homogeneity of OMP and DNA profiles of strains isolated from systemic sites strongly suggests the existence of clonal relationships betw een virulent strains and also suggests that expression of certain OMP profi les may be related to virulence.