Pili (fimbriae) of Branhamella species

Pili (fimbriae) have frequently been found to be involved in the attachment of bacteria to mucosal epithelial cells, an important initial step in the disease process. The purpose of this study was to determine if Branhamella catarrhalis expresses type 4 pili.

Piliated B. catarrhalis phenotypic characteristics of colony morphology, agar corrosion, twitching motility, competence for deoxyribonucleic acid (DNA) transformation, autoagglutination, and pellical formation were observed. DNA was isolated from Branhamella spp. and used in genomic Southern hybridizations with a Moraxella bovis pilin gene as a probe. Electron microscopy of negatively stained bacteria was carried out to visualize pili.

B. catarrhalis has several (but not all) of the phenotypic characteristics that are related to the presence of type 4 (MePhe) pili in closely related Moraxella spp., including competence for DNA transformation, autoagglutination, pellicle formation, colony morphology, and pitting of agar. The one phenotype we have not found that is generally characteristic of type 4 piliated bacteria is twitching motility. Genomic Southern hybridization analysis using a cloned M. bovis Q pilin gene as a probe reveals DNA homologous to the Q pilin gene in B. catarrhalis, Branhamella ovis, Branhamella caviae, and Branhamella cuniculi. Examination of B. catarrhalis strain ATCC25240 by electron microscopy reveals two different kinds of pili. One kind appears similar to other type 4 pili, whereas a second class is short pili extending outward from all portions of the bacteria.

Phenotypic, electron-microscopic, and hybridization data are all consistent with type 4 pili being present on some B. catarrhalis strains.