Inhibition of the β-Lactamases of Branhamella catarrhalis by Clavulanic Acid and Other Inhibitors

The β-lactamases of Branhamella catarrhalis Ravasio and strain 1908 were readily inhibited by low concentrations of sulbactam, β-halopenicillanic acids, MM 13902 and clavulanic acid. More detailed studies on the interaction of the Ravasio β-lactamase with clavulanic acid demonstrated that the enzyme had high affinity for the inhibitor (Ki= 0.07 µmol/L) and was rapidly inhibited (t½ = 21 sec, kinhib. = 0.033/sec). Two types of enzyme-inhibitor complex were formed, a transiently stable species (t½ = 5.3 minutes at pH 7.3 and 37°C) and a more stable species (t½ ≈ 2 hours at pH 7.3 and 37°C). Irreversible inactivation of the enzyme was not achieved.