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

Also, an orphan response regulator revSC21 was determined by the same research group. 155 This regulator revSC21 positively modulates expression levels of virulence factors (e.g., mrp, sly, and cps) and is required for bacterial pathogenesis. 155 In contrast, Pan et al. reported another orphan response regulator CovR with an opposite effect on S. suis pathogenicity. 30 The covR-defective (ΔcovR) mutant displayed thicker capsules and increased hemolytic activity. Furthermore, adherence of this mutant to epithelial cells was greatly increased, as well as its resistance to phagocytosis and killing by neutrophils and monocytes. Eventually, the removal of covR gene was found to be correlated with increased lethality of piglets, relative to those inoculated with its parent virulent strain 05ZYH33. 30 Others VirA is a newly-determined virulence factor that is exclusively present in virulent SS2 strain. 122 Trigger factor is also a virulence determinant which acts by controlling expression of a collection of known virulence factors, such as cps, mrp, and sly. 159 FeoBA encoding an iron transporter system might represent the first example of the fact that the machinery of a transporter can be involved in S. suis pathogenicity. 35 After Li et al. 28 defined transposal characteristics of 89K PAI in epidemic strain of Chinese virulent SS2, Hu's group recently obtained further insights into 89K PAI. In addition to virulence-determining element, salK-salR TCS system, 89K PAI also carried a second virulence factor, virD4-virB4, a type IV-like secretion system. Unexpectedly, this T4SS-like system is responsible for stimulating host immune reaction observed in mice infected with Chinese streptococcal toxic shock-like syndrome (STSLS)-causing strain of S. suis 2 160 , raising a possible relationship of 89K to molecular/immunological machinery by which this non-group A streptococcus (GAS), SS2 to cause STSLS in infected patients (Fig. 4) . Finally, Wilson et al. also suggested that 05SSU0660, an uncharacterized protein homologous to S. pneumonia spr1018 might be a virulence factor. 100