Influence of beta-lactamase-producing strains of Branhamella catarrhalis and Haemophilus influenzae on certain beta-lactam antibiotics.

Ampicillin, benzylpenicillin, cefaclor and cefuroxime were exposed to strains of Branhamella catarrhalis and Haemophilus influenzae with and without ability to produce beta-lactamase. The antibiotics were dissolved in phosphate buffer at pH 6, 7 and 8 and the mean enzyme activity was calculated from decrease in peak heights by the HPLC technique. Cefuroxime was the most stable drug regardless of pH. For the other antibiotics, changes in pH influenced the results. In infectious processes factors like pH and pCO2 show some variation. This fact may influence the interaction between beta-lactams and beta-lactamases.