Evaluation of the immunogenicity and the protective efficacy of a novel identified immunogenic protein, SsPepO, of Streptococcus suis serotype 2

► The sequence of SsPepO is highly conserved in S. suis 2. ► rSsPepO confer significant protection against challenge of S. suis 2 in mice and pigs. ► rSsPepO could elicit a strong humoral antibody response. ► rSsPepO also confer significant protection in passive immunization experiments. ► Our findings suggest that rSsPepO would be a promising subunit vaccine candidate.