Characterization of neurologic disease-associated Streptococcus suis strains within the United States swine herd and use of diagnostic tools

Authors: SANTOS STREAUSLINA, JESSICA - Iowa State University; Nielsen, Daniel; SCHWARTZ, KENT - Iowa State University; DERSCHEID, RACHEL - Iowa State University; MAGSTADT, DREW - Iowa State University; BURROUGH, ERIC - Iowa State University; GAUGER, PHILLIP - Iowa State University; SCHUMACHER, LONI - Iowa State University; RAHE, MICHAEL - Iowa State University; MICHAEL, ALYONA - Iowa State University; SITTHICHAROENCHAI, PANCHAN - Iowa State University; SIEPKER, CHRISTOPHER - Iowa State University; FERREYRA, FRANCO - Iowa State University; DE ALMEIDA, MARCELO NUNES - Iowa State University; MAIN, RODGER - Iowa State University; BRADNER, LAURA - Iowa State University; HU, XIAO - Iowa State University; LI, GANWU - Iowa State University; POETA SILVA, ANA PAULA - Iowa State University; SAHIN, ORHAN - Iowa State University; Arruda, Bailey

Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2024
Publication Date: 10/8/2024
Citation: Santos Streauslina, J., Nielsen, D.W., Schwartz, K.J., Derscheid, R.J., Magstadt, D.R., Burrough, E.R., Gauger, P.C., Schumacher, L.L., Rahe, M.C., Michael, A., Sitthicharoenchai, P., Siepker, C.L., Ferreyra, F.M., De Almeida, M., Main, R., Bradner, L.K., Hu, X., Li, G., Poeta Silva, A.S., Sahin, O., Arruda, B.L. 2024. Characterization of neurologic disease-associated Streptococcus suis strains within the United States swine herd and use of diagnostic tools. Journal of Clinical Microbiology. 62(11). Article e00374-24. https://doi.org/10.1128/jcm.00374-24.
DOI: https://doi.org/10.1128/jcm.00374-24

Interpretive Summary: Streptococcus suis negatively impacts swine health, posing diagnostic and preventative challenges. S. suis can induce disease and quietly reside on mucosal surfaces. This duality and the diagnostic tools routinely used to identify S. suis disease-associated strains further impedes a deeper understanding of this important pathogen. This study evaluated 2,379 S. suis central nervous system (CNS) isolates from diagnostic cases over a 5 year period. Isolates originating from cases with inflammation in CNS tissue at the cellular level (n = 1,032) were further characterized employing both standard and advanced diagnostic techniques. We identified all 29 S. suis serotypes, in addition to four reclassified serotypes as putative causes of CNS disease. Among these, serotypes 1 and 7 emerged as predominant putative causes of CNS infection (32% of cases). Sequencing and analysis of the whole genome of 145 S. suis isolates revealed that five commonly used virulence-associated genes (VAGs) were not present in the majority of disease-associated isolates and a commonly used diagnostic tool called matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF) misidentified multiple isolates. These data indicate that clinical signs and site of isolation alone are insufficient to call an isolate disease-associated, S. suis serotypes associated with CNS infection are more diverse than previously reported, MALDI-TOF may need to be supplemented with additional diagnostic tools for precise S. suis identification, and VAGs remain an unreliable means of defining S. suis isolates.

Technical Abstract: Streptococcus suis negatively impacts swine health, posing diagnostic and preventative challenges. S. suis can induce disease and quietly reside on mucosal surfaces. The complex ecology of S. suis and the diagnostic tools routinely used to identify S. suis disease-associated strains further impedes a deeper understanding of this important pathogen. This study evaluated 2,379 S. suis central nervous system (CNS) isolates from diagnostic cases between 2015 and 2019. Isolates originating from cases with histologic evidence of CNS infection (n = 1,032) were further characterized employing both standard and advanced diagnostic techniques. We identified all 29 S. suis serotypes, in addition to four reclassified serotypes as putative causes of CNS disease. Among these, serotypes 1 and 7 emerged as predominant putative causes of CNS infection (32% of cases). Furthermore, 51 sequence types (STs) of which 15 were novel were detected with ST1 predominating. Through whole-genome sequencing of 145 S. suis isolates, we observed that five commonly used virulence-associated genes (VAGs; epf, mrp, sly, ofs, and srtF) were not present in the majority of disease-associated isolates and matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF) misidentified multiple isolates. These data indicate that clinical signs and site of isolation alone are insufficient for defining a pathotype, S. suis serotypes and STs associated with CNS infection are more diverse than previously reported, MALDI-TOF may need to be supplemented with additional diagnostic tools for precise S. suis identification, and VAGs remain an unreliable means of defining S. suis isolates.