Ability of newer beta-lactam antibiotics to induce beta-lactamase production inEnterobacter cloacae

The beta-lactamase inducing properties of various new beta-lactam antibiotics in two isogenic strains ofEnterobacter cloacae were investigated. Beta-lactamase activity was measured two hours after addition of inducer to cells in the late logarithmic growth-phase. Beta-lactamase expression was highly dependent on the growth medium used, highest levels being obtained after induction with cefoxitin in Tryptic Soy broth, Mueller-Hinton broth and Nutrient broth. Upon induction the mutant 908 S_si produced tenfold higher beta-lactamase levels than its parent wild type 908 S_wi. Among the new antibiotics investigated, sulfoxides of several oxyimino-cephalosporins, HR 810, cefetamet, cefteram, carumonam and BRL 36650 were moderate or poor inducers. The penem FCE 22101 resembled imipenem in its strong inducing properties.