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. 2021 Dec;10(1):1960-1974.
doi: 10.1080/22221751.2021.1988725.

Genomic and pathogenic investigations of Streptococcus suis serotype 7 population derived from a human patient and pigs

Pujun Liang  1 , Mingliu Wang  2 , Marcelo Gottschalk  3 , Ana I Vela  4 , April A Estrada  5 , Jianping Wang  1 , Pengcheng Du  6 , Ming Luo  7 , Han Zheng  1 , Zongfu Wu  8
Affiliations

Genomic and pathogenic investigations of Streptococcus suis serotype 7 population derived from a human patient and pigs

Pujun Liang et al. Emerg Microbes Infect. 2021 Dec.

Abstract

Streptococcus suis is one of the important emerging zoonotic pathogens. Serotype 2 is most prevalent in patients worldwide. In the present study, we first isolated one S. suis serotype 7 strain GX69 from the blood culture of a patient with septicemia complicated with pneumonia in China. In order to deepen the understanding of S. suis serotype 7 population characteristics, we investigated the phylogenetic structure, genomic features, and virulence of S. suis serotype 7 population, including 35 strains and 79 genomes. Significant diversities were revealed in S. suis serotype 7 population, which were clustered into 22 sequence types (STs), five minimum core genome (MCG) groups, and six lineages. Lineages 1, 3a, and 6 were mainly constituted by genomes from Asia. Genomes of Lineages 2, 3b, and 5a were mainly from Northern America. Most of genomes from Europe (41/48) were clustered into Lineage 5b. In addition to strain GX69, 13 of 21 S. suis serotype 7 representative strains were classified as virulent strains using the C57BL/6 mouse model. Virulence-associated genes preferentially present in highly pathogenic S. suis serotype 2 strains were not suitable as virulence indicators for S. suis serotype 7 strains. Integrative mobilizable elements were widespread and may play a critical role in disseminating antibiotic resistance genes of S. suis serotype 7 strains. Our study confirmed S. suis serotype 7 is a non-negligible pathotype and deepened the understanding of the population structure of S. suis serotype 7, which provided valuable information for the improved surveillance of this serotype.

Keywords: Streptococcus suis serotype 7; integrative mobilizable elements; phylogeny; virulence; zoonotic pathogens.

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Conflict of interest statement

No potential conflict of interest was reported by the author(s).

Figures

Figure 1.
Figure 1.
A maximum-likelihood phylogenetic tree of 114 S. suis serotype 7 genomes. The phylogenetic tree was constructed based on mutational SNPs differences across the whole core genome. The S. pneumoniae ATCC 700669 was used as an outgroup to root the tree. The strains were coloured based on the isolation regions, grey for Europe, orange-yellow for North America, and orange-red for China. The scale is given as the number of substitutions per variable site.
Figure 2.
Figure 2.
The distribution of AR genes in MGEs and non-MGEs regions of S. suis serotype 7 genomes. The inner circle is the distribution of ICEs, IMEs, and CIMEs in S. suis serotype 7 genomes. Each panel of boxes filled with different colors represents ICEs, IMEs, and CIMEs integrated into the different locus of corresponding genomes, and hollow boxes represent the absence of ICEs, IMEs, or CIMEs in corresponding genomes. The middle circle showed the AR genes carried by ICEs, IMEs, or CIMEs. Each filled circle represents the corresponding AR gene present on corresponding ICEs, IMEs, or CIMEs. The outer circle showed the AR genes located into non-MGEs regions in S. suis serotype 7 genomes. Each filled star represents the corresponding AR gene present on non-MGEs regions in corresponding genomes.
Figure 3.
Figure 3.
The schematic comparison of the cps gene cluster subtype Ia to that of Ib (A), II (B), and III (C). Each colored arrow represents the gene whose predicted function is shown in the blow panel. HG17, HG18, HG19, HG72, and HG73 genes are indicated. The aroA gene is located on the 3′ side of each locus. Regions of over 70% identity were marked by blue shading.
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Grants and funding

This work was supported by the National Science and Technology Major Project from the Ministry of Health of the People's Republic of China [grant number 2017ZX10303405-002] and the National Natural Science Foundation of China [grant number 81572044].

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