Protection induced in pigs previously infected by the non-virulent strain 1330 of Streptococcus suis serotype 2 is not due to the secretion of the bacteriocin suicin

Authors: Hau, Samantha; FITTIPALDI, NAHUEL - University Of Montreal; PAYEN, SERVANE - University Of Montreal; GRENIER, DANIEL - University Of Laval; Nielsen, Daniel; Brockmeier, Susan; GOTTSCHALK, MARCELO - University Of Montreal

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2025
Publication Date: 5/29/2025
Citation: Hau, S.J., Fittipaldi, N., Payen, S., Grenier, D.W., Nielsen, D.W., Brockmeier, S., Gottschalk, M. 2025. Protection induced in pigs previously infected by the non-virulent strain 1330 of Streptococcus suis serotype 2 is not due to the secretion of the bacteriocin suicin. PLOS ONE. 20(5). Article e0323370. https://doi.org/10.1371/journal.pone.0323370.
DOI: https://doi.org/10.1371/journal.pone.0323370

Interpretive Summary: Streptococcus suis is a bacteria commonly found in the respiratory tract of pigs. It can also severe disease and death in pigs. S. suis costs the swine industry millions of dollars annually. Swine farmers control S. suis with antibiotic treatments and vaccines that prevent disease. Currently, there are no commercially available S. suis vaccines. Farmers use autogenous vaccines, which contain killed bacteria isolated from the specific farm. Autogenous vaccines often only prevent disease caused by the strain used in the vaccine. This leaves the pigs vulnerable to other S. suis strains on the farm. Swine farmers and veterinarians need new vaccines that can prevent disease with multiple strains of S. suis. This study tested vaccination with a live, non-disease-causing S. suis strain (90-1330). 90-1330 produces a bacteriocin which is a small protein that can kill other S. suis strains. Bacteriocins can improve bacterial survival and help them compete with other bacteria. Because 90-1330 produces a bacteriocin, it can kill disease causing S. suis strains and it may enhance its ability to prevent disease. Pigs vaccinated with 90-1330 did not show signs of disease 21 days after vaccination; however, 3 days after vaccination, pigs were still susceptible to S. suis disease. The role of the bacteriocin was also tested using a mutant strain that does not produce the bacteriocin (90-1330'suicin). The mutant strain was also able to prevent disease 21 days after vaccination, but not 3 days after vaccination. Both strains caused an increase in antibody titers 21 days after vaccination, showing protection against disease was likely due to immune stimulation and not the bacteriocin production. This work shows the promise of live vaccines against S. suis. It provides a new option for swine farmers to prevent S. suis disease and reduce the use of antibiotic treatments for S. suis. Better control of S. suis could result in significant cost savings for the swine industry.

Technical Abstract: Streptococcus suis is a systemic pathogen of swine and imposes a significant economic burden on the swine industry. Disease with S. suis is controlled with antibiotic treatment and vaccination with inactivated vaccines, which can be derived from the strains circulating on the farm. Inactivated vaccines have shown mixed results with minimal data supporting reductions in morbidity and mortality following their use. With increasing restrictions on antibiotic use and increasing concerns surrounding antimicrobial resistance, alternatives to antibiotics or novel, highly effective vaccines are needed for treating or preventing disease with S. suis. Bacteriocins are a potential alternative to antibiotics, as bacteriocins are antimicrobial peptides produced by bacteria. However, the use of bacteriocins to limit pathogenic S. suis remains relatively under-examined. Live vaccines are a potential novel and effective method of preventing disease, as they provide competition for pathogenic strains and would limit pathogenic strain colonization while stimulating a protective immune response. This study investigated the use of an avirulent, bacteriocin producing isolate of S. suis (90-1330) as an intranasal vaccine and evaluated the role of the bacteriocin by comparing protection to animals inoculated with a mutant lacking bacteriocin production (90-1330'suicin). Animals were protected from systemic disease when challenged with a virulent isolate 21 days after inoculation with either 90-1330 or 90-1330'suicin but were not protected when challenged 3 days after inoculation. Evaluation of antibody titers showed increased titers 21 days post-inoculation, and the humoral response was likely providing systemic protection. Although 90-1330 was unable to protect animals challenged 3 days post-inoculation, the strain should be considered a good candidate for vaccine development. S. suis 90-1330 was able to induce a protective immune response with a single intranasal inoculation and bacteriocin production may be able to contribute to protection when animals have a lower exposure dose, as in a production setting.