Serological cross-reactions between Moraxella (Branhamella) catarrhalis and other oropharyngeal bacteria

Oropharyngeal bacteria belonging to different species were tested for serological cross-reactions with Moraxella catarrhalis using sera from immunized rabbits. Sera were tested using immunofluorescence, an enzyme immunoassay (EIA) and immunoblotting. On immunofluorescence, significant cross-reactions were demonstrated with beta-hemolytic streptococci group A and group G, as well as with streptococci of the viridans group. Some cross-reactions were also noted with Neisseria meningitidis. In the EIA, strong cross-reactions were demonstrated with beta-hemolytic streptococci. No cross-reactions were obtained with Streptococcus pneumoniae, Haemophilus influenzae or common oral Neisseria. The results are of importance for the interpretation of serological tests to detect infections with Moraxella catarrhalis, and for the development of methods for detection of antigens in samples from the respiratory tract.