Comparison of the Outer Membrane Proteins of 50 Strains of Branhamella catarrhalis

Branhamella catarrhalis colonizes the respiratory tract of humans and commonly causes otitis media in children and respiratory infections in adults with chronic lung disease. In view of the emergence of this organism as an important human pathogen, we used sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to examine the outer membrane proteins (OMPs) of 50 strains of B. catarrhalis. OMPs were isolated from broth culture supernatants. Typical of other gram-negative bacteria, eight proteins ranging in molecular weight (MW) from ~98 000 to 21 000 daltons were revealed by SDSPAGE; these proteins were designated OMP A-OMP H. Of the OMPs identified, four were heat modifiable (C, D, E, and H). The 50 strains were obtained from diverse geographic and clinical sources. The OMP patterns were strikingly homogeneous; there was minimal variability in the MW of OMPs between strains. Future studies should establish whether the similarity in MWs of OMPs is paralleled by their antigenic characteristics.