Novel Capsular Polysaccharide Loci and New Diagnostic Tools for High-Throughput Capsular Gene Typing in Streptococcus suis

Abstract

Streptococcus suis is an important pathogen of pigs and may cause serious disease in humans. Serotyping is an important tool for detection and epidemiological studies of S. suis. Thirty-three reference serotypes and nine novel cps loci (NCLs) are recognized in S. suis. To gain a better understanding of the prevalence and genetic characteristics of NCLs, we investigated the serotype identity of 486 isolates isolated between 2013 and 2015 in China by capsular gene typing methods. Two hundred seventy-six isolates carried NCLs belonging to 16 groups, 8 of which appear to have not been reported previously. These isolates showed autoagglutination, polyagglutination, or nonagglutination with reference antisera and thus were nonserotypeable. Almost all isolates carrying the unknown NCLs were encapsulated, with various capsular thicknesses, indicating that they are most likely novel serotypes. To simultaneously identify the currently recognized 17 NCLs, an 18-plex detection system using the Luminex xTAG universal array technology was developed. Our data also provide valuable genetic information for monitoring the variations within NCLs by investigating the genetic characteristics of different subtypes within NCLs. IMPORTANCENonserotypeable Streptococcus suis isolates have been reported in many studies, and 9 novel cps loci (NCLs) have already been identified in nonserotypeable isolates. Moreover, novel cps loci are continually being found. The main purpose of this study was to investigate the prevalence and characteristics of NCLs in S. suis isolates recovered between 2013 and 2015 in China. This study provides valuable genetic information for monitoring the variations within NCLs. Meanwhile, a fast and cost-effective 18-plex detection system that can simultaneously identify the currently recognized 17 NCLs was developed in this study. This system will serve as a valuable tool for detecting known and identifying additional novel cps loci among nonserotypeable S. suis isolates. Streptococcus suis is an important pathogen of pigs and may cause serious disease in humans (1-3). Clinically healthy pigs can carry S. suis in their nasopharynx, contributing to the dissemination of this pathogen (4, 5). Moreover, a potential role of isolates from healthy pigs is as donors to transfer the new adaptive phenotypes to pathogenic isolates (6). The capsular polysaccharide (CPS) shields S. suis from host phagocytes and is a major virulence factor (7). Antisera to CPSs are used to distinguish antigenic differences among them. Serotyping is also an important epidemiological method for S. suis surveillance. This reflects the importance of including isolates from healthy pigs to better understand the diversity and evolution of CPSs in S. suis populations.A total of 35 serotypes (types 1 through 34 and type 1/2) of S. suis have been identified by different studies in the 1980s and 1990s (8-11). In 2005, strains of serotypes 32 and 34 were reclassified as Streptococcus orisratti (12). The CPS synthesis genes are known to be clustered ...

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

“…showed that eight lung isolates belonged to NCL1, NCL3, NCL4 and NCL11, indicating that these strains might be virulent. Further, they also demonstrated that isolates belonging to NCL1, NCL3, NCL4, NCL11 and Chz were prevalent in swine population in China and therefore, suggested increasing the surveillance on these NCLs‐harboured isolates (Qiu et al., ). Zheng et al.…”

“…Isolates were identified as S. suis strains by the presence of S. suis ‐specific genes recN and gdh (Ishida et al., ; Okwumabua, O'Connor, & Shull, ), and then were further confirmed by 16S rRNA sequence. PCR assays were used to identify the 29 serotypes (Liu et al., ), NCL1‐8 (Zheng et al., ), NCL9‐16 (Qiu et al., ), NCL17‐20 (Zheng et al., ) and Chz (Pan et al., ). The isolates that were non‐typeable by PCR assays were selected for further research.…”

“…Recently, a new variant serotype Chz was identified from piglets with meningitis (Pan et al, 2015). In addition, 20 novel cps loci (NCL) in total were identified (designated as NCL1-20) from non-typeable isolates (Qiu, Bai, Lan, Zheng, & Xu, 2016;Zheng et al, 2015Zheng et al, , 2017. It has been shown that strains carrying NCLs were widely distributed in non-typeable isolates from both healthy and diseased pigs (Qiu et al, 2016;Zheng et al, 2017).…”

Genotyping and investigating capsular polysaccharide synthesis gene loci of non-serotypeable Streptococcus suis isolated from diseased pigs in Canada

“…Thus, high-throughput capsular gene typing systems based on serotype-specific wzy genes have become attractive alternatives/complement to the existing serological tests [ 18 , 20 , 21 ]. However, even with the use of multiplex PCR tests, non-serotypeable strains are still commonly isolated from both clinically healthy and diseased animals [ 18 , 22 , 23 ].…”

“…In recent years, 17 novel cps loci (NCLs) were identified from non-serotypeable S. suis and were designated as NCL1 to 16 and serotype Chz [ 22 – 24 ]. Meanwhile, an 18-plex Luminex assay was also developed to detect these 17 NCLs and nearly 60% of non-serotypeable strains from healthy pigs carried one of these NCLs [ 22 ]. However, little is known about the distribution and characteristics of the cps loci of potentially virulent non-serotypeable strains recovered from diseased animals.…”