Peptidyl isomerase PrsA is surface-associated on Streptococcus suis and offers cross-protection against serotype 9 strain

PrsA, a peptidyl isomerase encoded by the prsA gene, plays pleiotropic roles in bacterial physiology and pathogenicity. This study was attempted to characterize the distribution of prsA in different serotypes of Streptococcus suis isolates and on the bacterial cells and to evaluate its immunogenicity in a murine model. PrsA is present in different S. suis types and surface-associated as tested in a S. suis type 2 strain. The prsA gene from the serotype 2 strain was cloned for its expression in Escherichia coli. Recombinant PrsA (SsPrsA) showed good reactivity with anti-sera to S. suis serotype 2 and 9 strains. Immunization of mice with SsPrsA elicited a significant antibody response and conferred partial protection against lethal challenge with a S. suis serotype 2 strain (50% protection) or a serotype 9 strain (66% protection). The anti-SsPrsA sera showed good reactivity to the surface-associated proteins of both serotype 2 and serotype 9 strains. Higher abundance of surface-associated PrsA in the serotype 9 strain (than the serotype 2 strain) might account, in part, for higher protection against its challenge infection. These results suggest that SsPrsA may serve as a novel subunit vaccine candidate with cross-protective potential.