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

Of particular note, SS2 seems to be a previously neglected but recently emerging human pathogen, 5 whose infection has become increasingly potent, especially in the southeast Asian countries like Thailand, 6 Vietnam, 7 and China. 8, 9 As the primary agent of meningitis, septicemia, arthritis and as an opportunistic pathogen in the case of pneumonia, 1, 5 S. suis have been reported to have spread over 30 countries and/ or regions (Fig. 1) and has claimed no less than 1600 human cases, some of which were fatal. 2 Also, similar clinical symptoms including bacterial meningitis, septicemia, and arthritis are frequently observed in human SS2 infections. 2, 3 Occasionally, serotypes other than SS2, including SS1, 10 SS4, 10 SS5, 11, 12 SS14, 13, 14 SS16, 15, 16 and SS24 11 can also be found to function as the causative agents responsible for sporadic cases of human S. suis infection. 3 Of note, two big outbreaks of human SS2 endemics which occurred in China, in 1998 and 2005, respectively, 9, 17, 18 have raised serious concerns in public health and have challenged the conventional opinion that human SS2 infections are only present in sporadic cases. 2, 8, 19 Unfortunately, no specific/effective human therapeutics or vaccine against SS2 infections is available thus far. Considering the severity (high mortality and modality) of SS2 infection in humans, 5, 8 it is important to develop a method for convenient and quick diagnosis, which can be applied toward local SS2 detection. 4, 18 Over the past four decades, significant progress has been made toward better understanding the highly infectious clones of S. suis. At the time of formulating this review, 1104 articles were available in PubMed regarding S. suis (http://www.ncbi.nlm.nih. gov/pubmed/?term=Streptococcus+suis).Totally, over 20 bacterial virulence-associated factors have been identified that include capsular polysaccharides (CPS), 20 Muramidase-released protein (MRP), 21 and Suilysin (SLY). 22 To date, genomic sequences of a collection of S. suis strains are available (Fig. 2) , the majority of which are derived from SS2 species, 23 ,24 except two newly-released genomes which correspond to SS3 25 and SS14, 26 respectively. Genomic mining combined with bacterial genetics have elucidated that Chinese epidemic strains of highly pathogenic S. suis 2 carry a specific 89K PAI (pathogenicity island). 23, 27 Further studies suggested that 89K PAI with a transposon-like essence can Streptococcus suis (S. suis) is a family of pathogenic grampositive bacterial strains that represents a primary health problem in the swine industry worldwide. S. suis is also an emerging zoonotic pathogen that causes severe human infections clinically featuring with varied diseases/syndromes (such as meningitis, septicemia, and arthritis). Over the past few decades, continued efforts have made significant progress toward better understanding this zoonotic infectious entity, contributing in part to the elucidation of the molecular mechanism underlying its high pathogenicity. This review is aimed at presenting an updated overview of this pathogen from the perspective of molecular epidemiology, clinical diagnosis and typing, virulence mechanism, and protective antigens contributing to its zoonosis.