| Streptococcus suis serotype 2 is a pathogen responsible for important economic losses in the swine industry. The infections caused by this microorganism are meningitis, septicemia, endocarditis, and arthritis. S. suis is also recognized as a zoonotic agent and its isolation from other animal species, including cattle and birds, is increasingly reported. Currently, the available information on pathogenesis of S. suis infections and on the virulence factors of S. suis remains very limited. It was also reported that S. suis can be present in the tonsils of pigs without clinical signs. These animals are considered healthy carriers, and immunization does not prevent bacterial adhesion to tonsils. The carriage of S. suis can last several weeks and can be responsible for the propagation of the bacteria through the herd. Bacterial adhesion to host cells is an important step in colonization process and it needs to be understood thoroughly in order to develop strategies to prevent the carrier state. The main objective of this study was to identify and characterize S. suis proteins involved in the bacterial adhesion, with a focus on a 39 kDa protein that was identified as a glyceraldehyde-3-phosphate dehydrogenase by its N-terminus sequence.; Mutants with hydrophobicity surface variations were obtained by transposition using Tn916 and were used in adhesion tests on tracheal cells and porcine tracheal rings. Following cellular adhesion assays, five clones showed a significant reduction in adhesion and their Tn916 insertion sites were characterized by inverse PCR. The valyl-tRNA synthetase and RecN protein genes were identified. Isogenic mutants, defective in the expression of the 39 kDa protein at the bacterial surface, were also tested and showed a significant decrease in adhesion compared to their wild type strain. The 39 kDa (GAPDH) encoding gene was identified and its complete sequence was obtained. A high homology between this protein and other GAPDH found in pathogenic streptococci was showed. Using S. suis GAPDH and a histidine tag, a fusion protein was generated and the protein was purified. We observed, using porcine tracheal rings preincubated with the purified protein, a significant reduction of S. suis adhesion. Therefore, the GAPDH protein seems to be involved in the adhesion of S. suis to the upper respiratory tract and could be considered as an adhesin. |
