DnaJ of Streptococcus suis Type 2 Contributes to Cell Adhesion and Thermotolerance.

To examine if the molecular chaperone DnaK operon proteins of Streptococcus suis type 2 (SS2) are involved in adhesion to host cells, the abundance values of these proteins from the surface of two SS2 strains of different adhesion capability were compared. Their roles in growth and adhesion to human laryngeal epithelial cell line HEp-2 cells were investigated on SS2 strain HA9801 and its mutants with DnaK operon genes partially knocked-out (PKO mutant) under heat stress. The major difference was that DnaJ was more abundant in strain HA9801 than in strain JX0811. Pretreatment of the bacteria with hyperimmune sera to DnaJ, but not with those to other proteins, could significantly reduce SS2 adhesion to HEp-2 cells. PKO of dnaJ g ene resulted in decreased SS2 growth at 37 °C and 42 °C, and reduced its adhesion to HEp-2 cells. The wild-type strain stressed at 42 °C had increased expression of DnaJ on its surface and elevated adhesion to HEp-2 cells, which was also inhibitable by DnaJ specific antiserum. These results indicate that the DnaJ of S. suis type 2 is important not only for thermotolerance but also for adhesion to host cells. Because DnaJ expression is increased upon temperature upshift with increased exposure on the bacterial surface, the febrile conditions of the cases with systemic infections might help facilitate bacterial adhesion to host cells. DnaJ could be one of the potential candidates as a subunit vaccine because of its good immunogenicity.

Heat incubation inactivates streptococcal exotoxins and recombinant cholesterol-dependent cytolysins: suilysin, pneumolysin and streptolysin O.

Streptococcus species release cholesterol-dependent cytolysins (CDCs), which are a main toxin, and their heat susceptibility is poorly understood. The aim of this study was to clarify the heat susceptibility of streptococcal exotoxins and CDCs. Streptococcal exotoxins were treated with heat incubation at 60 °C for 10 or 30 min. The Streptococcus suis exotoxin of serotypes 1 and 2 exhibited more than 50 % haemolytic activity, and all Streptococcus pneumoniae exotoxins exhibited more than 60 % haemolytic activity. During the thermolabile assay, the virulent streptococcal haemolytic activity remarkably decreased after being heated at 60 °C for 10 m. Then, streptococcal recombinant CDCs were produced and put through a thermolabile assay. The haemolytic activity of suilysin (SLY), pneumolysin (PLY) and streptolysin O (SLO) decreased more than 80 % after heat incubation. We also conducted a TER assay to evaluate the cell monolayer. The cell monolayer of all CDCs broke down, and the FITC-dextran translocated at 1 h post addition, while the CDCs treated with heating did not induce cell disruption. Moreover, the microscopy analysis demonstrated that CDCs treated with heating lost their activity. In conclusion, heat incubation induced the inactivation of streptococcal exotoxins and CDCs. Heat incubation plays a role in the degradation of the streptococcal exotoxin, and this result applies to the inhibition of streptococcal infection.