Unravelling the unique essential genes of Streptococcus canis through transposon-directed insertion-site sequencing.

Streptococcus canis represents a major canine pathogen, accounting for 22.4% of streptococcal infections in dogs. However, despite its prevalence in veterinary medicine, the mechanisms underlying S. canis pathogenesis and survival remain poorly understood. Identifying targeted treatments against S. canis could help to reduce dysbiosis-related complications and minimize the selection of resistant neighbouring bacteria. In this study, we employed transposon-directed insertion-site sequencing for the first time to generate saturated mutant libraries of S. canis. By comparing three distinct strains, we defined the shared essential genome of this pathogen. We found that 90.4% of its essential genes are also present in the essential genomes of other related pyogenic streptococcal species, including Streptococcus pyogenes, Streptococcus agalactiae and Streptococcus equi subsp. equi, demonstrating the translational relevance of S. canis research to broader streptococcal biology. Notably, we identified two genes uniquely essential to S. canis at the terminal steps of glycolysis: ldh, which governs lactate metabolism, and pta, which catalyses the conversion of acetyl-CoA to acetyl phosphate in acetate metabolism. We propose that targeting these pathways may offer a novel, species-specific therapeutic strategy for treating S. canis infections.