Haemophilus parainfluenzae has a limited core lipopolysaccharide repertoire with no phase variation.

Cell surface lipopolysaccharide (LPS) is a well characterized virulence determinant for the human pathogen Haemophilus influenzae, so an investigation of LPS in the less pathogenic Haemophilus parainfluenzae could yield important insights. Using a panel of 18 commensal H. parainfluenzae isolates we demonstrate that the set of genes for inner core LPS biosynthesis largely resembles that of H. influenzae, with an additional heptosyltransferase I gene similar to waaC from Pasteurella multocida. Inner core LPS structure is therefore likely to be largely conserved across the two Haemophilus species. Outer core LPS biosynthetic genes are much less prevalent in H. parainfluenzae, although homologues of the H. influenzae LPS genes lpsB, non-phase variable lic2A and lgtC, and losA1, losB1 and lic2C are found in certain isolates. Immunoblotting using antibodies directed against selected LPS epitopes was consistent with these data. We found no evidence for tetranucleotide repeat-mediated phase variation in H. parainfluenzae. Phosphocholine, a phase variable H. influenzae LPS epitope that has been implicated in disease, was absent in H. parainfluenzae LPS as were the respective (lic1) biosynthetic genes. The introduction of the lic1 genes into H. parainfluenzae led to the phase variable incorporation of phosphocholine into its LPS. Differences in LPS structure between Haemophilus species could affect interactions at the bacterial-host interface and therefore the pathogenic potential of these bacteria.

Structural characterization of Haemophilus parainfluenzae lipooligosaccharide and elucidation of its role in adherence using an outer core mutant.

The opportunistic pathogen Haemophilus parainfluenzae is a gram-negative bacterium found in the oropharynx of humans. Haemophilus parainfluenzae is a member of the Pasteurellaceae family in which it is most closely related to Haemophilus sengis and Actinobacillus. Characterization of surface displayed lipooligosaccharide has identified components that are crucial in adherence. We examined the oligosaccharide structure of lipooligosaccharide from 2 clinical isolates of H. parainfluenzae. Core oligosaccharide was isolated by standard methods from purified lipooligosaccharide. Structural information was established by a combination of monosaccharide and methylation analyses, nuclear magnetic resonance spectroscopy, and mass spectrometry revealing the following structures: R-(1-6)-beta-Glc-(1-4)-D,D-alpha-Hep-(1-6)-beta-Glc-(1-4)- substituting a tri-heptose-Kdo inner core of L,D-alpha-Hep-(1-2)-L,D-alpha-Hep-(1-3)-L,D-alpha-Hep-(1-5)-alpha-Kdo at the 4-position of the proximal L,D-alpha-Hep residue to Kdo, and with a PEtn residue at the 6-position of the central L,D-alpha-Hep residue. In strain 4282, the R substituent is beta-galactose and in strain 4201 there is no substituent at the distal glucose. These analyses have revealed that multiple structural aspects of H. parainfluenzae lipooligosaccharide are comparable with nontypeable Haemophilus influenzae lipooligosaccharide. This study also identified a galactan in strain 4201 and a glucan in strain 4282. Haemophilus parainfluenzae was shown to adhere to a bronchial epithelial cell line to the same degree as nontypeable H. influenzae. However, an H. parainfluenzae mutant lacking the outer core of the lipooligosaccharide showed diminished adherence to the epithelial cells, suggesting that H. parainfluenzae lipooligosaccharide plays a role in tissue colonization.