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

Fast/effective detection and analyses of S. suis is critical for the prevention and/or diagnosis of endemic S. suis 2 infection in the swine industry as well as for S. suis infected patients. Three types of experimental approaches are available thus far that consist of (1) selective media-based microbiological cultivation, (2) molecular tests, and (3) immunological assays ( Table 1) . Given its advantage in sensitivity and fastness, the second method has been experimentally developed into two subgroups (PCR-based detection plus typing-oriented analyses like pulsed-field gel electrophoresis [PFGE] and restriction fragment length polymorphism [RFLP]) and might be potential in clinical re-confirmation and/ or re-valiadtion. Generally, PCR assays can be classified into six kinds among which multiplex-PCR (using sets of specific primers including epf, mrp, and gdh) is appreciably-valid approach to assay SS2 and applied in some countries ( Table 1) . The major four kinds of typing methods include PFGE, RFLP, multi-locus sequence typing (MLST) and random amplified polymorphic DNA (RAPD), some of which have derivatives such as ISR-RFLP ( Table 1 ). In general, the three experimental methods (PFGE, RFLP, and RAPD) can return clues about genomic differences between different strains/serotypes. Given direct sequencing of multiple loci (cpn60, dpr, recA, aroA, thrA, gki, and mutS), MLST can directly capture the nucleotide sequence deviation used for typing purpose. Among the immunological approaches, ELISA could be the most popular way to address S. suis infection in some experimental tests ( Table 1) . In fact, different versions of ELISA have been developed that are based on various capture antigens identified to be specifically against S. suis 2. We have also established two kinds ELISA assays (one is based on SAO protein, 4,36 the other is based on Enolase surface antigen 96 ), both of which work well in our trials during field screening and clinical detections. Recently, two more new derivative methods were reported, which are immunochromatographic strip 97,98 and electrochemiluminescence immunosensor, 99 respectively ( Table 1) .