Streptococcus suis serotype 2 collagenase-like protease promotes meningitis by increasing blood–brain barrier permeability

Streptococcus suis serotype 2 (SS2) is an emerging zoonotic pathogen that causes meningitis in humans and pigs. This pathogen generates substantial economic losses in the swine industry while posing a significant threat to public health security. The mechanisms through which SS2 penetrates the brain and induces meningitis remain incompletely understood. This study examines the role and mechanism of SS2 collagenase-like protease (Clp) in facilitating bacterial passage across the blood–brain barrier (BBB). The research demonstrates that SS2 Clp enhanced virulence and tissue colonization while promoting BBB degradation in mice. The Δclp mutant exhibited reduced ability to traverse human brain microvascular endothelial (hCMEC/D3) cell monolayers compared to wild-type SS2, while the addition of recombinant protein rClp increased permeability. Furthermore, rClp significantly enhanced SS2 adhesion to hCMEC/D3, suppressed the expression of intercellular tight junction proteins ZO-1, Occludin, and Claudin-5 independent of its enzyme activity, and triggered hCMEC/D3 apoptosis through cell receptor ligand apoptosis and mitochondrial apoptosis pathways, partially dependent on its enzyme activity, leading to BBB disruption and enhanced permeability. Additionally, Clp enhanced the infiltration of macrophages (F4/80+), monocytes (F4/80-Ly6C+), and neutrophils (Ly6G+) into the brain following SS2 infection. These findings establish that SS2 Clp is essential for bacterial passage across the BBB, offering a theoretical foundation for improved prevention and treatment strategies for SS2-induced meningitis.