Streptococcus suis infection: An emerging/reemerging challenge of bacterial infectious diseases?

Feng, Youjun; Zhang, Huimin; Wu, Zuowei; Wang, Shihua; Cao, Min; Hu, Dan; Wang, Changjun

Development of a safe and efficient vaccine is a useful strategy to combat against S. suis infection. In contrast to conventional killed/live whole-bacteria vaccines, [168] [169] [170] engineering of subunit vaccine exhibits significant advantage in its safety and its largescale producibility. 171 Identification of protective antigens is a prerequisite for identifying candidate vaccine molecules. Totally, there are no less than 15 protective antigens identified thus far ( Table 3) . Among them, four molecules of protective antigen are well-known virulence associated factors and are MRP, EF, 38 kDa, and SLY ( Table 3) . Of note, most of the remaining 10 protein antigens were elucidated by research groups in China. In 2009, in addition to identification of the known protective antigen SLY, Liu's report verified three more new protective antigens that are RTX family exoprotein A (RfeA), epidermal surface antigen (ESA), and immunoglobulin G (IgG)-binding protein (IBP). 172 Two different research groups from China confirmed that enolase, an enzyme of central metabolism, acts as a protective antigen displayed on bacterial surface. 96, 129 However, Esgleas and coworker 130 reported an opposite result regarding the protective efficiency of enolase in mice. This discrepancy could be due to different versions of recombinant protein, different strains plus deviations in animal vaccination protocols. In particular note, all the three newly-identified immunogenic antigens (6PGD, HP0197, and HP245) are elucidated by the same Chen's research group in China (Table 3) .