Virulence Studies of Different Sequence Types and Geographical Origins of Streptococcus suis Serotype 2 in a Mouse Model of Infection

Abstract

Multilocus sequence typing previously identified three predominant sequence types (STs) of Streptococcus suis serotype 2: ST1 strains predominate in Eurasia while North American (NA) strains are generally ST25 and ST28. However, ST25/ST28 and ST1 strains have also been isolated in Asia and NA, respectively. Using a well-standardized mouse model of infection, the virulence of strains belonging to different STs and different geographical origins was evaluated. Results demonstrated that although a certain tendency may be observed, S. suis serotype 2 virulence is difficult to predict based on ST and geographical origin alone; strains belonging to the same ST presented important differences of virulence and did not always correlate with origin. The only exception appears to be NA ST28 strains, which were generally less virulent in both systemic and central nervous system (CNS) infection models. Persistent and high levels of bacteremia accompanied by elevated CNS inflammation are required to cause meningitis. Although widely used, in vitro tests such as phagocytosis and killing assays require further standardization in order to be used as predictive tests for evaluating virulence of strains. The use of strains other than archetypal strains has increased our knowledge and understanding of the S. suis serotype 2 population dynamics.

Streptococcus suis serotype 2 strains isolated in Argentina (South America) are different from those recovered in North America and present a higher risk for humans

“…However, important differences in virulence of isolates within this serotype have been described (Auger et al , 2016). It has been shown that Eurasian strains generally present a higher virulence potential than those from Canada and the USA, two countries that together are the second most important swine producers worldwide after China (Gottschalk, 2012).…”

Structural analysis and immunostimulatory potency of lipoteichoic acids isolated from three Streptococcus suis serotype 2 strains

“…are considered low virulent and have been mostly associated with secondary infections and immunocompromised individuals (8,9). Consequently, we chose ST1, ST7, and ST25 strains for our analyses because of their importance as predominant virulent S. suis serotype 2 strains, which are responsible for most porcine and human infections worldwide (3).…”

Inflammatory Monocytes and Neutrophils Regulate Streptococcus suis-Induced Systemic Inflammation and Disease but Are Not Critical for the Development of Central Nervous System Disease in a Mouse Model of Infection

“…As previously described, S. suis induced high plasmatic levels of the different proinflammatory mediators measured (interleukin-6 [IL-6], IL-12p70, interferon-␥ [IFN-␥], C-C motif chemokine ligand 3 [CCL3], CCL4, CCL5, C-X-C motif chemokine ligand 2 [CXCL2], and CXCL9) in wild-type mice (Fig. 2) (4,35). Levels of these mediators in the plasma of Nr4a1 Ϫ/Ϫ mice were similar to those of wild-type mice (Fig.…”

“…Though host death during the S. suis systemic infection is usually due to an exacerbated inflammatory response, a certain level of inflammation is required for bacterial elimination (10). As such, the role of monocytes in systemic inflammation was evaluated by measuring plasma mediators from wild-type, CCR2 Ϫ/Ϫ , and Nr4a1 Ϫ/Ϫ mice 12 h postinfection, corresponding to the time when production is maximal (4,35). As previously described, S. suis induced high plasmatic levels of the different proinflammatory mediators measured (interleukin-6 [IL-6], IL-12p70, interferon-␥ [IFN-␥], C-C motif chemokine ligand 3 [CCL3], CCL4, CCL5, C-X-C motif chemokine ligand 2 [CXCL2], and CXCL9) in wild-type mice (Fig.…”