Characterization of cell-bound papain-soluble beta-lactamases in BRO-1 and BRO-2 producing strains of Moraxella (Branhamella) catarrhalis and Moraxella nonliquefaciens

In Moraxella (Branhamella) catarrhalis and Moraxella nonliquefaciens strains isolated from clinical specimens in the south of Sweden two variants of beta-lactamase were distinguished by isoelectric focusing (IEF). The BRO-1 (Ravasio type) enzyme was the most common in Branhamella catarrhalis, constituting about 90% of the beta-lactamase found in this species, while the BRO-2 enzyme (1908 type) was as common as BRO-1 in Moraxella nonliquefaciens. The determinants mediating the production of BRO-1 and BRO-2 were both transferable by conjugation. Cell-bound beta-lactamase from reference strains producing BRO-1 and BRO-2 could be solubilized by papain digestion. The isoelectric point of the solubilized enzymes differed distinctly between BRO-1 (pI 6.5) and BRO-2 (pI 6.9). The molecular species of BRO-1 and BRO-2 released by papain digestion were purified by affinity chromatography with phenylboronic acid agarose gel. They had identical molecular weights of approximately 28,000. Their kinetic constants were indistinguishable for a number of substrates and beta-lactamase inhibitors.