The major heat-modifiable outer membrane protein CD is highly conserved among strains of Branhamella catarrhalis.

The outer membrane of Branhamella catarrhalis contains a major, heat-modifiable outer membrane protein called CD which has epitopes on the surface of the intact bacterium. The gene encoding CD was cloned and expressed in Escherichia coli. The protein migrates in gels as a doublet, indicating that CD is encoded by single gene whose gene product has two stable conformations. The nucleotide sequence of the gene encoding CD was determined and shows homology with the OprF outer membrane protein of Pseudomonas species. The CD protein contains a proline-rich region, which appears to account for its aberrant migration in gels. Restriction fragment-length analysis of 30 isolates of B. catarrhalis with oligonucleotide probes corresponding to sequences in the CD gene produced identical patterns in Southern blot assays. The major heat-modifiable outer membrane protein CD shares homology with the OprF protein and is highly conserved among strains of B. catarrhalis.