Outer membrane vesicles shield Moraxella catarrhalis [Beta]-lactamase from neutralization by serum IgG

The aim of this study was to detect the presence of IgG against Moraxella catarrhalis ...-lactamase in healthy adults, and to determine whether outer membrane vesicles (OMVs) could protect the enzyme from inhibition by anti-...-lactamase IgG. Transmission electron microscopy was used to detect the presence of ...-lactamase in OMVs. Sera were examined by ELISA for specific IgG directed against recombinant M. catarrhalis ...-lactamase in addition to the outer membrane adhesins MID/Hag, UspA1 and A2. Binding of anti-...-lactamase IgG from serum to OMVs was analysed by flow cytometry. The chromogenic substrate nitrocefin was used to quantify ...-lactamase enzyme activity. The presence of ...-lactamase was determined in OMVs from a 9-year-old child suffering from M. catarrhalis sinusitis. Furthermore, anti-...-lactamase IgG was detected in sera obtained from healthy adults. Out of 40 adult blood donors (aged 18-65 years) tested, 6 (15.0%) carried anti-...-lactamase IgG. No correlation between IgG titres against ...-lactamase and the adhesins was found. Flow cytometry analyses revealed that anti-...-lactamase IgG from serum bound to ...-lactamase-positive OMVs. By comparing the ...-lactamase activity of intact OMV with OMV that were permeabilized with saponin we found that OMVs shielded active ...-lactamase from the anti-...-lactamase IgG. Moraxella catarrhalis ...-lactamase is found in, or associated with, OMVs, providing clinical relevance for the vesicles in the spread of antibiotic resistance. Furthermore, OMVs protect ...-lactamase from specific IgG. (ProQuest: ... denotes formulae/symbols omitted.)