NlpI Contributes to Escherichia coli K1 Strain RS218 Interaction with Human Brain Microvascular Endothelial Cells

Escherichia coli K1 is the most common Gram-negative bacillary organism causing neonatal meningitis.E. coli K1 binding to and invasion of human brain microvascular endothelial cells (HBMECs) is a prerequisite for its traversal of the blood-brain barrier (BBB) and penetration into the brain. In the present study, we identified NlpI as a novel bacterial determinant contributing toE. coli K1 interaction with HBMECs. The deletion ofnlpI did not affect the expression of the known bacterial determinants involved inE. coli K1-HBMEC interaction, such as type 1 fimbriae, flagella, and OmpA, and the contribution of NlpI to HBMECs binding and invasion was independent of those bacterial determinants. Previous reports have shown that thenlpI mutant ofE. coli K-12 exhibits growth defect at 42°C at low osmolarity, and its thermosensitive phenotype can be suppressed by a mutation on thespr gene. ThenlpI mutant of strain RS218 exhibited similar thermosensitive phenotype, but additionalspr mutation did not restore the ability of thenlpI mutant to interact with HBMECs. These findings suggest the decreased ability of thenlpI mutant to interact with HBMECs is not associated with the thermosensitive phenotype. NlpI was determined as an outer membrane-anchored protein inE. coli , and thenlpI mutant was defective in cytosolic phospholipase A2 α (cPLA2 α) phosphorylation compared to the parent strain. These findings illustrate the first demonstration of NlpI's contribution toE. coli K1 binding to and invasion of HBMECs, and its contribution is likely to involve cPLA2 α.