Lmb, a protein with similarities to the LraI adhesin family, mediates attachment of Streptococcus agalactiae to human laminin

Streptococcus agalactiae is a leading cause of neonatal sepsis and meningitis. Adherence to extracellular matrix proteins is considered an important factor in the pathogenesis of infection, but the genetic determinants of this process remain largely unknown. We identified and sequenced a gene which codes for a putative lipoprotein that exhibits significant homology to the streptococcal LraI protein family. Mutants of this locus were demonstrated to have substantially reduced adherence to immobilized human laminin. The nucleotide sequence of the gene was subsequently designated Imb (laminin binding) and shown to be present in all of the common serotypes of S. agalactiae. To determine the role of Lmb in the adhesion of S. agalactiae wild-type strains to laminin, a recombinant Lmb protein harboring six consecutive histidine residues at the C terminus was cloned, expressed, and purified from Escherichia coli. Preincubation of immobilized laminin with recombinant Lmb significantly reduced adherence of the wild-type strain O90R to laminin. These results indicate that Lmb mediates the attachment of S. agalactiae to human laminin, which may be essential for the bacterial colonization of damaged epithelium and translocation of bacteria into the bloodstream.