Molecular Characterization of the β-Lactamases from Clinical Isolates of Moraxella ( Branhamella ) catarrhalis Obtained from 24 U.S. Medical Centers during 1994–1995 and 1997–1998

The β-lactamases from 403 Moraxella ( Branhamella ) catarrhalis clinical isolates obtained during 1994–1995 and 1997–1998 U.S. multicenter surveillance studies were characterized by isoelectric focusing. The overall prevalences of the BRO-1 and BRO-2 enzymes among β-lactamase-positive isolates were estimated to be 97.5 and 2.5%, respectively. The minimum inhibitory concentrations (MICs) of ampicillin for all BRO-2-producing isolates were ≤1 μg/ml; however, numerous β-lactamase-positive isolates for which the ampicillin MICs were ≤1 μg/ml produced the BRO-1 enzyme (88.1%).