A novel pilus-associated gene cluster is implicated in Streptococcus agalactiae virulence.

Streptococcus agalactiae (S. agalactiae), also known as Group B Streptococcus (GBS), is an important zoonotic pathogen. It is an important pathogen that causes bovine mastitis and can also lead to severe infections in newborns, pregnant women, and individuals with a weakened immune system. Adhesion to host cells is the first critical step in S. agalactiae infection, making the identification of key adhesion-related genes essential for understanding the pathogenic mechanisms of GBS. In this study, we used the Tn transposon system to construct a mutant library of S. agalactiae A909 and employed the mouse mammary epithelial cell line EPH4-Ev as a model to screen and validate adhesion-related genes. Our results revealed a gene cluster containing BP, AP1, and SrtC. While these genes did not affect the basic biological characteristics of the bacteria, they significantly influenced the adhesion rate to cells and the virulence of A909 in mice. Further transcriptomic analysis revealed that the Tnfsf15 gene plays a critical role in the regulation of A909 strain pathogenicity mediated by the BP, AP1, and SrtC gene clusters during host infection.