The evolving story of Streptococcus gallolyticus: classification, pathogenesis, role in human and animal disease, and laboratory diagnostics

Streptococcus gallolyticus , formerly known as S. bovis , belongs to the Streptococcus bovis / Streptococcus equinus complex (SBSEC). Besides being a part of the gut microbiome, this organism has gained interest due to its association with infective endocarditis and its strong correlation with colorectal cancer in humans. In veterinary medicine, systemic infection caused by S. gallolyticus has been reported in various animal populations, including porcine, ruminant, and avian species. Despite its clinical importance in humans and animals, two key challenges persist: the limited understanding of the pathogenesis due to its ubiquitous nature and inconsistencies in diagnostic laboratory reporting of the bacteria in SBSEC. This review summarizes the taxonomic characterization of the SBSEC, its clinical manifestations across species, current understanding of the bacterial pathogenesis, and the laboratory diagnostic assays used for its detection. We will further discuss the importance of SBSEC speciation and subspeciation, highlighting their distinct clinical implications and potential impact on human and animal health.