Anti-Biofilm Potential of Phage SS2 against Streptococcus suis

Streptococcus suis serotype 2 is considered a major pathogen causing diseases worldwide in both humans and swine. In pigs, S. suis leads to highly invasive infections, including meningitis, arthritis, endocarditis, bronchopneumonia, septicemia, and sudden death. S. suis is a heterogeneous organism with multiple serotypes and sequence types, exhibiting different virulence patterns and a diverse geographical distribution of serotypes that has resulted in vaccination failures at the field level. In this study, we isolated lytic phages against S. suis serotype 2, which could have therapeutic potential by reducing biofilm-forming ability and combating antibiotic-resistant strains of S. suis. A lytic bacteriophage, named SS2 phage, was recovered from sewage. Samples were collected at a piggery farm. Bacteriophage SS2 showed a larger plaque size (4 mm diameter) and the highest mean phage titre (14 log PFU/ml). The antibiofilm effect was tested against S. suis biofilm; a phage titre of 1x109 PFU/ml (i.e., MOI 10) was found to inhibit biofilm formation with a significant reduction in biofilm biomass (OD595 from 2.56 to 1.01) on the crystal violet staining assay. Our study provides a detailed analysis of the role of phage SS2 as an anti-biofilm potential against S. suis, which could be a natural therapeutic strategy against antimicrobialresistant S. suis strains.