CsiR-mediated signal transduction pathway in response to low iron conditions promotes Escherichia coli K1 invasion and penetration of the blood-brain barrier.

Escherichia coli K1 is the leading cause of neonatal Gram-negative bacterial meningitis, but the pathogenesis of E. coli K1 meningitis remains unclear. Blood-brain barrier (BBB) penetration is a crucial step in E. coli meningitis development. Here, we uncovered the crucial role of CsiR, a GntR family regulator, in E. coli K1 virulence. During infection, csiR expression was induced due to the derepression by Fur in the blood and human brain microvascular endothelial cells (HBMECs). CsiR positively regulated ilvB expression, which is associated with branched chain amino acid synthesis. Furthermore, we revealed that IlvB activated the FAK/PI3 K pathway of HBMECs to induce actin cytoskeleton rearrangements, thereby promoting the bacterial invasion and penetration of the BBB. Overall, this study reveals a CsiR-mediated virulence regulation pathway in E. coli K1, which may provide a useful target for the prevention or therapy of E. coli meningitis.