Assessment of complement-mediated killing of Moraxella (Branhamella) catarrhalis isolates by a simple method

Abstract

Recently, we showed that complement resistance is an important virulence factor of Moraxella (Branhamella) catarrhalis. Our study used a serum bactericidal assay to determine complement resistance in M. catarrhalis. Although the serum bactericidal assay is considered the ''gold standard'' for determining complement resistance, it is laborious and time-consuming and therefore not well suited for large-scale studies. Using a large number (n ‫؍‬ 324) of M. catarrhalis isolates obtained from the sputa of patients with lower respiratory tract infections (n ‫؍‬ 200) and young carriers (n ‫؍‬ 124), we assessed the value of a simple ''culture-and-spot'' test as an alternative to the serum bactericidal assay. For both groups of isolates, the degree of concordance between the two tests used was very significant (P < 0.0001). The agreement between the two assays was estimated to be ''excellent beyond chance'' (as determined by Cohen's kappa test). The culture-and-spot assay is a valuable alternative to the serum bactericidal assay, not only for screening purposes as shown here but also for studying the mechanism of complement resistance in M. catarrhalis at the molecular level.

Phage Antibodies Obtained by Competitive Selection on Complement-ResistantMoraxella(Branhamella)catarrhalisRecognize the High-Molecular-Weight Outer Membrane Protein

“…Complement resistance. M. catarrhalis strains were subdivided into three groups according to their sensitivity to serum complement-mediated lysis as described previously (37): resistant (survival of more than 50% of the bacteria during a 3-h incubation in 50% human pooled serum), sensitive (less than 3% survival after incubation for 1 h in 50% pooled human serum), and with intermediate survival.…”

Moraxella catarrhalisis only a weak activator of the mannose-binding lectin (MBL) pathway of complement activation

“…Five isolates of M. catarrhalis were tested for MBL activating capacity, all obtained from children who suffered recurrent acute otitis media episodes. Three isolates (isolates 2040-1, 3001-14/20 and 4017-7) had been previously determined to be complement resistant and 2 isolates complement sensitive (isolates 3053-14 and 3007-7) via a simple ''spot and drop'' test [6,7].…”

Complement-resistant Moraxella catarrhalis forms a genetically distinct lineage within the species

“…Complement-resistant phenotypes were established in duplicate using a microtitre bactericidal assay and a serum spot test [18]. The strains were divided into three di¡erent groups, complement-sensitive (n = 28), complement-resistant (n = 44) and intermediately resistant (n = 3).…”