Monoclonal antibody against lipooligosaccharide of Moraxella catarrhalis decreases resistance to aminopenicillins

The following Moraxella catarrhalis strains were used in the experiments: eight beta-lactamase-producing clinical isolates and four isolates including a control strain 353 CCUG without beta-lactamase. The other strains used as controls in this procedure were two isolates of Staphylococcus aureus and two of Escherichia coli: beta-lactamase producers and non-producers control strains of S. aureus: ATTC 29213 and E. coli ATCC 25922. All of the microbial strains were tested with ampicillin alone and with ampicillin in combination with murine monoclonal antibody (MAb) 219 against lipooligosaccharide of M. catarrhalis in a 96-well plate to determine the minimal inhibitory concentration (MIC). The testing was performed by broth dilution method and minimal bactericidal concentration (MBC) on brain heart infusion agar (BHI). The effect of the combination of aminopenicillin with MAb219 was manifested as a fourfold reduction of the MIC and the MBC of the tested beta-lactamase producing M. catarrhalis. The effect over the control strains and moraxellae without beta-lactamase was either missing or there was a slight reduction of MIC and MBC. The conclusion of the study is that MAb219 in combination with ampicillin in in vitro testing can decrease resistance to aminopenicillins in M. catarrhalis after the linking of MAb219 with lipooligosaccharide of the outer membrane in the antigen-antibody complex.