Genetic analysis of the diversity in outer membrane protein P2 of non-encapsulated Haemophilus influenzae.

The molecular basis for the diversity of the major outer membrane protein (MOMP) P2 of non-encapsulated Haemophilus influenzae was analyzed by direct sequencing of fragments of the P2 genes, obtained by the polymerase chain reaction. Genetically divergent H. influenzae strains were isolated from patients with otitis media and from infected patients with chronic obstructive pulmonary disease (COPD). The nucleotide sequences of these P2 genes were determined and compared with P2 gene sequences of three non-encapsulated strains and with the P2 gene of encapsulated H. influenzae type b. Variation in the nucleotide sequence of the P2 genes of non-encapsulated H. influenzae was localized in eight distinct regions which were interchanged with relatively conserved regions. Regions 2, 4, 5 and 8 were found to be hypervariable, since they were characterized by multiple deletions or substitutions of nucleotides. According to the proposed structure of MOMP P2 the variable regions were localized in eight loop structures exposed at the outside of the outer membrane. Loops 2, 4, 5 and 8 were hypervariable in all isolates whereas loop 6 varied only in isolates from COPD patients with persistent infections.