The population structure, antimicrobial resistance, and pathogenicity of Streptococcus suis cps31
Xiaoming Wang1, Junjie Sun1, Chen Bian2
1MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
Abstract:
Streptococcus suis is a zoonotic pathogen that can cause invasive infections in humans and pigs. The S. suis cps31 strains (SS31) were frequently isolated from healthy or diseased pigs and one human infection case caused by SS31 was reported in Thailand in 2015. However, except for a few epidemiologic studies, little information is available for SS31. To characterize SS31, a total of 75 SS31 strains were analyzed, including 52 strains that were isolated from healthy or diseased pigs and 23 strains whose information was accessed from NCBI. The MLST analysis showed that SS31 exhibited high heterogeneity. The phylogenetic analysis and minimum core-genome (MCG) classification revealed that 75 strains were clustered into 3 lineages. Strains from NCBI mainly at Lineage 2 belong to MCG7-3, and most of strains from China at Lineage 3 belong to MCG7-2. This finding indicated that their evolutionary path was different. All SS31 strains were resistant to more than three classes of antimicrobial agents, and major antimicrobial resistance genes for strains from Lineage 3 were carried by prophages. This observation is different from the previous observation that integrative conjugative elements and integrative and mobilizable elements are major vehicles of antimicrobial resistance genes for S. suis. In addition to strains isolated from diseased pigs, seven of 47 strains isolated from clinically healthy pigs were also pathogenic in a zebrafish infection model. These findings reveal unique characteristics of SS31 and contribute to establishing public health surveillance for SS31 and clarifying the diversity of S. suis.
Insights
Streptococcus suis cps31 (SS31) strains show genetic diversity and antimicrobial resistance. Some SS31 strains from healthy pigs are pathogenic, highlighting the need for public health surveillance.
Area of Science:
- Microbiology
- Genomics
- Zoonotic Diseases
Background:
- Streptococcus suis is a zoonotic pathogen causing invasive infections in humans and pigs.
- S. suis cps31 (SS31) strains are frequently isolated but poorly characterized.
- A human SS31 infection case was reported in Thailand in 2015.
Purpose of the Study:
- To characterize the genetic diversity and antimicrobial resistance of SS31 strains.
- To investigate the pathogenicity of SS31 strains in a zebrafish model.
- To inform public health surveillance strategies for SS31.
Main Methods:
- Multilocus Sequence Typing (MLST) analysis of 75 SS31 strains.
- Phylogenetic analysis and Minimum Core-Genome (MCG) classification.
- Antimicrobial resistance profiling and identification of resistance genes.
- Pathogenicity testing in a zebrafish infection model.
Main Results:
- SS31 strains exhibited high genetic heterogeneity, clustering into 3 distinct lineages.
- Antimicrobial resistance was observed across all SS31 strains, with Lineage 3 strains carrying resistance genes on prophages.
- Seven of 47 SS31 strains from clinically healthy pigs demonstrated pathogenicity in zebrafish.
Conclusions:
- SS31 strains possess unique evolutionary paths and distinct antimicrobial resistance gene mechanisms.
- Pathogenic SS31 strains can be present in clinically healthy pigs, posing a potential public health risk.
- Findings underscore the importance of continued surveillance and characterization of S. suis diversity.
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