COMPLEMENT RESISTANCE IS A VIRULENCE FACTOR OF BRANHAMELLA (MORAXELLA) CATARRHALIS

The purpose of this study was to investigate complement resistance in Branhamella (Moraxella) catarrhalis isolated from healthy schoolchildr en or sputum-producing adult patients. Two techniques were used: a ser um bactericidal assay as the gold standard and an easier 'culture and spot' test. Children (age 4-13; n = 303) and patients (n = 1047) showe d high colonization/infection rates with B. catarrhalis (31% and 19%, respectively). Complement resistance or intermediate sensitivity occur red frequently in patient isolates (62% and 27%, respectively) and les s often in children (33% and 8.5%, respectively; P much less than 0.00 01). In young children (age 4-5 years), the proportion of complement-r esistant strains was around 50%. Complement resistance in B. catarrhal is is associated with illness and may hence be considered a virulence factor.