MOLECULAR CHARACTERIZATION OF THE BRO BETA-LACTAMASE OF MORAXELLA (BRANHAMELLA) CATARRHALIS

A rapid increase in the prevalence of beta-lactamase-producing Moraxel la (Branhamella) catarrhalis strains has been noticed during the last decades, Today, more than 80% of strains isolated worldwide produce be ta-lactamase. To investigate beta-lactamase(s) of M. catarrhalis at th e molecular level, the BRO-1 beta-lactamase gene (bla) was isolated as part of a 4,223-bp HindIII fragment, Sequence analysis indicated that bla encodes a polypeptide of 314 amino acid residues, Insertional ina ctivation of bla in M. catarrhalis resulted in complete abrogation of beta-lactamase production and ampicillin resistance, demonstrating tha t bra is solely responsible for beta-lactam resistance. Comparison wit h other beta-lactamases suggested that M. catarrhalis beta-lactamase i s a unique enzyme with conserved residues at the active sites, The pre sence of a signal sequence for lipoproteins suggested that it is lipid modified at its N terminus, In keeping with this assumption was the o bservation that 10% of beta-lactamase activity was found in the membra ne compartment of M. catarrhalis. M. catarrhalis strains produce two t ypes of beta-lactamase, BRO-1 and BRO-2, which differ in their isoelec tric points, The BRO-1 and BRO-2 genes from two ATCC strains of M. cat arrhalis were sequenced, and only one amino acid difference was found between the predicted products, However, there was a 21-bp deletion in the promoter region of the BRO-2 gene, possibly explaining the lower level of production of BRO-2, The G+C content of bla (31%) was signifi cantly lower than those of the flanking genes (47 and 50%), and the ov erall G+C content of the M. catarrhalis genome (31%), These results in dicate that bla was acquired by horizontal gene transfer from another, still unknown species.