1986 Volume 36 Issue 1 Pages 59-70
The induction of β-lactamase and β-lactam resistance in Enterobacter cloacae were studied using clinical isolates and mutants with altered activity or inducibility of β-lactamase.
The majority of clinical strains tested were able to produce β-lactamase inducibly and the amount of increase of enzyme production was 20-to 350-fold in the presence of an inducer (ampicillin). The production of β-lactamase began to increase within 10 minutes after addition of the inducer and the increase continued linearly for at least 1 hour in exponentially growing cells. The amount of induced enzyme paralleled the drug concentration used.
The inducer activities of different β-lactams were different from each other and did not directly relate to the stability against the induced β-lactamase or to the M I C of the β-lactams.Even β-lactamase-susceptible drugs like piperacillin showed low MICs on the inducible strain when these drugs showed no inducer- activity for β-lactamase production. The results obtained revealed that the antibacterial activity of a β-lactam in E. cloacae is a sum of the following 4 activities : 1) permeability into the cell, 2) inhibitory activity against the target proteins (penicillin-binding proteins), 3) resistance to β-lactamase, and 4) inducibility of β-lactamase.
