Increased beta-lactamase activity in Branhamella catarrhalis after exposure to amoxicillin and clavulanic acid.

Branhamella catarrhalis, previously regarded as a harmless member of the normal nasopharyngeal flora, has periodically been implicated as the major pathogen in representative cases of a variety of infections such as sinusitis, pneumonia, septicemia and meningitis. In addition, beta-lactamase production of these microorganisms, first described in 1977, has been reported with increasing frequency, up to 80%. The first-choice drug for the therapy of the infections caused by beta-lactamase producing strains of B. catarrhalis is amoxicillin combined with clavulanic acid. The aim of our work was to determine the influence of amoxicillin and clavulanic acid on the biosynthesis of beta-lactamase of B. catarrhalis. Our results point out that the combination of amoxicillin and clavulanic acid produces only a slight increase in enzyme activity in 5003 and 462 strains. Clavulanic acid alone caused no increase in enzyme production. Ravasio strain showed no increase in enzyme formation after exposure to antibiotics.