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. 2024 Feb 6;55(1):17.
doi: 10.1186/s13567-024-01270-5.

Characterization of pig tonsils as niches for the generation of Streptococcus suis diversity

Kai Kobayashi  1 , Hiroaki Kubota  2 , Mari Tohya  3   4 , Megumi Ushikubo  5 , Miki Yamamoto  5 , Tsukasa Ariyoshi  2 , Yumi Uchitani  2 , Morika Mitobe  2 , Rumi Okuno  2 , Ichiro Nakagawa  6 , Tsutomu Sekizaki  6   7 , Jun Suzuki  2 , Kenji Sadamasu  2
Affiliations

Characterization of pig tonsils as niches for the generation of Streptococcus suis diversity

Kai Kobayashi et al. Vet Res. .

Abstract

Streptococcus suis is a gram-positive bacterium that causes meningitis, septicemia, endocarditis, and other disorders in pigs and humans. We obtained 42 and 50 S. suis isolates from lesions of porcine endocarditis and palatine tonsils, respectively, of clinically healthy pigs in Japan; we then determined their sequence types (STs) by multilocus sequence typing (MLST), cps genotypes, serotypes, and presence of classical major virulence-associated marker genes (mrp, epf, and sly). The 42 isolates from endocarditis lesions were assigned to a limited number of STs and clonal complexes (CCs). On the other hand, the 50 isolates from tonsils were diverse in these traits and seemingly in the degree of virulence, suggesting that tonsils can accommodate a variety of S. suis isolates. The goeBURST full algorithm using tonsil isolates obtained in this study and those retrieved from the database showed that major CCs as well as many other clusters were composed of isolates originating from different countries, and some of the STs were very similar to each other despite the difference in country of origin. These findings indicate that S. suis with not only different but also similar mutations in the genome have survived in tonsils independently across different geographical locations. Therefore, unlike the lesions of endocarditis, the tonsils of pigs seemingly accommodate various S. suis lineages. The present study suggests that S. suis acquired its diversity by natural mutations during colonization and persistence in the tonsils of pigs.

Keywords: MLST; Streptococcus suis; clonal complex; cps genotype; porcine endocarditis; serotype; tonsil; virulence-associated markers.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
The scheme of the present study design
Figure 2
Figure 2
goeBURST analysis using all S. suis isolates described in this study and all strains retrieved from the PubMLST database (2273 STs) at the triple-locus variant level visualizing clonal complexes. A-1–A-3 Major clonal complexes related to each other. ST117 is related to ST28 via ST27 (i.e., a double-locus variant of ST28) and is included in CC28. ST1528 is linked to ST87 at the double-locus variant level, and is included in CC87. ST1529 is related to ST94 via ST108 (i.e., a triple-locus variant of ST94) and is included in CC94. B Independent CCs and Singletons
Figure 3
Figure 3
MLST-based minimal spanning tree of 50 S. suis isolates from tonsils described in this study and 559 isolates of tonsil origins in the database. The tree was calculated using the goeBURST full algorithm. Numbers within the nodes indicate the corresponding sequence type. Node colors refer to the origin of countries as represented in the remarks. Numbers on lines indicate locus variants between nodes
See this image and copyright information in PMC

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