RELATIVE EFFICACY OF TAZOBACTAM, SULBACTAM AND CLAVULANIC ACID IN ENHANCING THE POTENCY OF AMPICILLIN AGAINST CLINICAL ISOLATES OF ENTEROBACTERIACEAE

Three beta-lactamase inhibitors were combined with ampicillin in a fix ed 2:1 ratio. The activity of ampicillin was enhanced by tazobactam an d by clavulanic acid, and to a lesser extent by sulbactam when tested against fresh clinical isolates of Enterobacteriaceae. At a concentrat ion of 8 mug/ml, ampicillin alone inhibited 49.6 % of 2,434 consecutiv e isolates of enteric bacilli compared to 81 % inhibited by ampicillin combined with tazobactam or clavulanic acid and 69.3 % inhibited by t he sulbactam/ampicillin combination. A four-fold or greater reduction in ampicillin MICs was observed in comparable numbers of isolates with all three combinations, but the most marked effects were seen with st rains that were highly resistant to ampicillin.