Streptococcus suis – The “Two Faces” of a Pathobiont in the Porcine Respiratory Tract

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.

Fatal case of bacteremia caused by Streptococcus suis in a splenectomized man and a review of the European literature

“…Although the colonization rate of S. suis in swine and wild boars is well-known and characterized (85-100%), the reports on the epidemiology of invasive S. suis infections in these animals in Europe (especially Hungary) are scarce [73]. Interestingly, while there is significant geographical variation in the prevalence of human S. suis cases (cases from Europe only account for about 8-9% of cases), the epidemiological variations in pig infections are far less pronounced [74].…”

Identification of six novel capsular polysaccharide loci ( NCL ) from Streptococcus suis multidrug resistant non‐typeable strains and the pathogenic characteristic of strains carrying new NCL s

“…As a normal colonizer of the upper respiratory tracts, S. suis is a typical respiratory pathobiont in swine, which possesses a highly invasive potential and could cause severe infectious diseases in pigs and humans (Votsch, Willenborg, Weldearegay, & Valentin-Weigand, 2018). The two phases (commensal and pathogenic) of this pathobiont in the porcine respiratory tract make it well-suited as an paradigmatic example for antimicrobial use and drug resistance in veterinary medicine (Seitz, Valentin-Weigand, & Willenborg, 2016;Votsch et al, 2018).…”

“…As a normal colonizer of the upper respiratory tracts, S. suis is a typical respiratory pathobiont in swine, which possesses a highly invasive potential and could cause severe infectious diseases in pigs and humans (Votsch, Willenborg, Weldearegay, & Valentin-Weigand, 2018). The two phases (commensal and pathogenic) of this pathobiont in the porcine respiratory tract make it well-suited as an paradigmatic example for antimicrobial use and drug resistance in veterinary medicine (Seitz, Valentin-Weigand, & Willenborg, 2016;Votsch et al, 2018). In this study, all six new NCL strains were resistant to clindamycin, lincomycin, erythromycin, tilmicosin and tetracycline (Table 2) and especially, the occurrence of high-level resistant strains to these antimicrobials in both pathogenic and commensal isolates (our unpublished data) may pose a concern to human health as pointed out by Varela et al (2013).…”

Examining the Effect of Host Recruitment Rates on the Transmission of Streptococcus suis in Nursery Swine Populations

“…While we can expect that higher probabilities are associated with more cases of clinical disease, the true value of p is likely influenced by several factors related to the host, pathogen, and environment. For instance, external factors that induce stress in piglets (e.g., weaning, mixing with other litters, overcrowding, and poor housing conditions) have been shown to correlate with increased clinical infections in the nursery [1,37,38]. Additionally, host-specific factors related to genetics, age, and immune status can also play a role in disease onset [39].…”

“…Given the limited understanding of the effects of sub-clinically infected pigs on S. suis disease occurrence, we only considered the clinical course of infection in the absence of sufficient data. Further, S. suis infections are known to be multi-factorial, where factors related to the host, pathogen, and system can impact the occurrence and severity of disease or morbidity in pigs [37]. As a result, there are limited empirical data on parameters that determine the natural course of this disease, therefore these parameters were estimated using model fitting.…”