ABSTRACTEscherichia 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 to
E. coli
K1 interaction with HBMECs. The deletion of
nlpI
did not affect the expression of the known bacterial determinants involved in
E. 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 the
nlpI
mutant of
E. coli
K-12 exhibits growth defect at 42°C at low osmolarity, and its thermosensitive phenotype can be suppressed by a mutation on the
spr
gene. The
nlpI
mutant of strain RS218 exhibited similar thermosensitive phenotype, but additional
spr
mutation did not restore the ability of the
nlpI
mutant to interact with HBMECs. These findings suggest the decreased ability of the
nlpI
mutant to interact with HBMECs is not associated with the thermosensitive phenotype. NlpI was determined as an outer membrane-anchored protein in
E. coli
, and the
nlpI
mutant was defective in cytosolic phospholipase A
2
α (cPLA
2
α) phosphorylation compared to the parent strain. These findings illustrate the first demonstration of NlpI's contribution to
E. coli
K1 binding to and invasion of HBMECs, and its contribution is likely to involve cPLA
2
α.