Abstract
Streptococcus (S.) suis is a frequent early colonizer of the upper respiratory tract of pigs. In fact, it is difficult to find S. suis-free animals under natural conditions, showing the successful adaptation of this pathogen to its porcine reservoir host. On the other hand, S. suis can cause life-threatening diseases and represents the most important bacterial cause of meningitis in pigs worldwide. Notably, S. suis can also cause zoonotic infections, such as meningitis, septicemia, endocarditis, and other diseases in humans. In Asia, it is classified as an emerging zoonotic pathogen and currently considered as one of the most important causes of bacterial meningitis in adults. The “two faces” of S. suis, one of a colonizing microbe and the other of a highly invasive pathogen, have raised many questions concerning the interpretation of diagnostic detection and the definition of virulence. Thus, one major research challenge is the identification of virulence-markers which allow differentiation of commensal and virulent strains. This is complicated by the high phenotypic and genotypic diversity of S. suis, as reflected by the occurrence of (at least) 33 capsular serotypes. In this review, we present current knowledge in the context of S. suis as a highly diverse pathobiont in the porcine respiratory tract that can exploit disrupted host homeostasis to flourish and promote inflammatory processes and invasive diseases in pigs and humans.
Highlights
Streptococcus (S.) suis is a commensal part of the respiratory microbiota of pigs, in particular of the tonsils and nasal cavities, but it can cause highly invasive infections, such as meningitis, arthritis, endocarditis, bronchopneumonia, as well as septicemia and sudden death (Arends et al, 1984; Feng et al, 2014; Segura et al, 2016)
We focus on the role of S. suis as a typical respiratory pathobiont in swine, which possesses a highly invasive potential and causes severe infectious diseases in pigs and humans
We focus on bacterial factors and mechanisms, which most likely are important for the commensal life of S. suis in the respiratory tract, though these factors may contribute to virulence (Figure 1, upper part)
Summary
Streptococcus (S.) suis is a commensal part of the respiratory microbiota of pigs, in particular of the tonsils and nasal cavities, but it can cause highly invasive infections, such as meningitis, arthritis, endocarditis, bronchopneumonia, as well as septicemia and sudden death (Arends et al, 1984; Feng et al, 2014; Segura et al, 2016). Though the colonization rate is up to 100%, clinical cases of S. suis infections, associated with meningitis, septicemia, or pneumonia, are by far less frequently reported (Goyette-Desjardins et al, 2014).
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