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

Accumulated data has suggested that no less than 20 bacterial enzymes might be implicated in the manifestation of S. suis virulence ( Table 2) . Among them, eight enzymes are proposed to be virulence factors by Wilson et al. 100 using the system of signature-tagged mutagenesis ( Table 2) . Four of them are generally regarded as enzymes of central metabolism, which separately correspond to (1) GlnA, glutamine synthetase, 127 (2) Gdh, glutamate dehydrogenase, 128 (3) enolase catalyzing dehydration of 2-phosphoglycerate to phosphor-enolpyruvate, 96, 129, 130 and (4) Impdh, inosine 5-monophosphate dehydrogenase. 131 Five of these enzymes are directly or indirectly related to synthesis and/ or modification of bacterial surface structure, including DltA, an enzyme catalyzing lipoteichoic d-alanylation, 132 PgdA, peptidoglycan N-acetylglucosamine deacetylase, 133 ApuA, a bifunctional amylopullulanase, 134 DPP IV, di-peptidyl peptidase IV, 135 and sortase A, a transpeptidase. 136, 137 One of the remaining two enzymes is IgA1 protease, which has highly immune-reactive activity to convalescent sera, 138 and the other is S-ribosylhomocycteinase (LuxS) catalyzing synthesis of auto-inducer 2 (AI-2) utilized in interspecies quorum sensing. 139, 140 As follows, we will discuss the roles of these enzymes in S. suis pathogenesis.