Digalactoside expression in the lipopolysaccharide of Haemophilus influenzae and its role in intravascular survival.

Digalactoside (galalpha-1-4 galbeta) structures of the lipopolysaccharide (LPS) of Haemophilus influenzae are implicated in virulence. A confounding factor is that tetranucleotide repeats within the lic2A, lgtC, and lex2 genes mediate phase-variable expression of the digalactosides. By deleting these repeats, we constructed recombinant strains of RM153 constitutively expressing either one or two LPS digalactosides.