Branhamella catarrhalis: antibiotic sensitivities and beta-lactamases

Twenty-eight strains of Branhamella catarrhalis, isolated from patients with acute exacerbations of chronic bronchitis, were tested both for beta-lactamase production and for sensitivity to a wide range of antimicrobial agents. A microtitre broth dilution technique was used for the latter and the MIC50, MIC90, and geometric mean MIC values were all calculated. Eleven strains were found to produce beta-lactamases. Isoelectric focusing in polyacrylamide gels showed four different band patterns, of which the most common was identical with that of the Ravasio type enzyme. Substrate profiles of the four types of branhamella beta-lactamases differed from each other although one was again similar to the Ravasio enzyme profile. Most of these beta-lactamases were readily inhibited by clavulanic acid (with I50 values of 0.01-0.08 mg/l) but were less readily inhibited by oxacillin. Attempts to isolate extrachromosomal DNA were unsuccessful. These results suggest that at least five possible different beta-lactamases can be demonstrated in Bran. catarrhalis strains, and that they are chromosomally determined.