Characterization of the plasmid-mediated β-lactamase in Branhamella catarrhalis, with special reference to substrate affinity

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Abstract
The plasmid-mediated Branhamella catarrhalis β-lactamase BRO-1, also found in Moraxella nonliquefaciens, was characterized as regards substrate profile, isoelectric point and relative substrate affinity index (RSAI) to various substrates and compared in these aspects with the TEM-1 enzyme of Haemophilus influenzae. As measured by a biological assay and with high performance liquid chromatography (HPLQ, BRO-1was found to hydrolyse carbenicillin, mecillinam, methicillin and cefaclor with a higher rate than TEM-1. The only substrates having a relative rate of hydrolysis higher for TEM-1 than for BRO-1 were ampicillin and cephaloridine. The rates of hydrolysis registered with these two methods wei-e comparable for all but 2 of 13 tested substrates. Isoelectric focusing yielded a main band at pH 5-6 and several satellite bands consistent with those reported by other authors for BranhameUa enzymes having a substrate profile similar to that of BRO-1. A tenfold or higher difference in SAI between BRO-1 and TEM-1 was recorded for five of the 15 compounds tested. BRO-1 seems to be the most common β-lactamase in Bran, catarrhalis, irrespective of geographic origin. Its substrate profile, isoelectric pattern and RSAI differ from those of other known plasmid-mediated β-lactamases described, thus justifying a specific esignation.