A membrane-bound precursor β-lactamase in strains of Moraxella catarrhalis and Moraxella nonliquefaciens that produce peripiasmic BRO-1 and BRO-2 β-lactamases

By employing the non-ionic detergent Triton X-100, a membrane-bound beta-lactamase was extracted from strains of Moraxella (Branhamella) catarrhalis and Moraxella nonliquefaciens that produce BRO-1 and BRO-2 beta-lactamases. Unlike BRO-1 and BRO-2, which exhibit multiple major bands on isoelectric focusing (IEF), the membrane-bound enzyme focused as a single IEF band at a pI of 6.20, which was not present with either of the other two enzymes. The membrane-bound beta-lactamase could be extracted from all strains producing BRO-1 and BRO-2, including recombinant strains constructed by transformation or conjugation. The enzyme was also recovered from Escherichia coli strain HB101 carrying vector plasmid pLQ521 into which the BRO-1 beta-lactamase gene from M. catarrhalis had been cloned. All three beta-lactamases were indistinguishable by inhibitor profiles with clavulanic acid, BRL 42715, sulbactam and tazobactam. These data suggested that all three beta-lactamases were the product of a single gene in Moraxella spp., and that the membrane-bound beta-lactamase serves as a precursor of both BRO-1 and BRO-2. Species differences in cellular processing of the membrane-bound enzyme could explain the minor differences in IEF patterns that occurred with BRO-1 and BRO-2 beta-lactamases when present in different species.