title: Outer membrane vesicles shield Moraxella catarrhalis β-lactamase from neutralization by serum IgG.
abstract: OBJECTIVE
  The aim of this study was to detect the presence of IgG against Moraxella catarrhalis β-lactamase in healthy adults, and to determine whether outer membrane vesicles (OMVs) could protect the enzyme from inhibition by anti-β-lactamase IgG.
  
  
  METHODS
  Transmission electron microscopy was used to detect the presence of β-lactamase in OMVs. Sera were examined by ELISA for specific IgG directed against recombinant M. catarrhalis β-lactamase in addition to the outer membrane adhesins MID/Hag, UspA1 and A2. Binding of anti-β-lactamase IgG from serum to OMVs was analysed by flow cytometry. The chromogenic substrate nitrocefin was used to quantify β-lactamase enzyme activity.
  
  
  RESULTS
  The presence of β-lactamase was determined in OMVs from a 9-year-old child suffering from M. catarrhalis sinusitis. Furthermore, anti-β-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-β-lactamase IgG. No correlation between IgG titres against β-lactamase and the adhesins was found. Flow cytometry analyses revealed that anti-β-lactamase IgG from serum bound to β-lactamase-positive OMVs. By comparing the β-lactamase activity of intact OMV with OMV that were permeabilized with saponin we found that OMVs shielded active β-lactamase from the anti-β-lactamase IgG.
  
  
  CONCLUSIONS
  Moraxella catarrhalis β-lactamase is found in, or associated with, OMVs, providing clinical relevance for the vesicles in the spread of antibiotic resistance. Furthermore, OMVs protect β-lactamase from specific IgG.
authors.affiliation: Medical Microbiology, Department of Laboratory Medicine Malmö,  Lund University, Skåne University Hospital, Malmö,  Sweden.
authors.forename: Viveka
authors.initials: V
authors.lastname: Schaar
authors.forename: Magnus
authors.initials: M
authors.lastname: Paulsson
authors.forename: Matthias
authors.initials: M
authors.lastname: Mörgelin
authors.forename: Kristian
authors.initials: K
authors.lastname: Riesbeck
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000907:Antibodies, Bacterial / Q000097:blood* / Q000378:metabolism; D057134:Antibodies, Neutralizing / Q000097:blood* / Q000378:metabolism; D002648:Child; D055354:Exosomes / Q000201:enzymology*; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D001936:Moraxella catarrhalis / Q000201:enzymology*; D009500:Neutralization Tests; D055815:Young Adult; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D000907:Antibodies, Bacterial; D057134:Antibodies, Neutralizing; D007074:Immunoglobulin G; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases