Résumé
The presence of a specific substrate will often induce or increase the enzymatic activity of cells towards that substrate. Cohen and Monod studied the transport of lactose [glucose- beta -D-galactoside] into Escherichia coli cells and postulated that the presence of an enzyme beta -galactosidase was required for its intracellular hydrolysis. Ortho-Nitrophenylgalactoporanoside [ONPG] and analogue of lactose was used in this study, since one can measure its transport into the cell as a consequence of its hydrolysis by an intracellular enzyme, beta -galactosidase. In order to relate the effect of ONPG on biochemical event to its bacteriostatic activity, the growth-inhibitory activity of this compound against Escherichia coli was investigated in the presence and absence of two inducers for beta -galctosidase enzyme namely, lactose and isopropyl thio- beta -D-galactosidase [IPTG]. In the presence of 1% lactose as an inducer, ONPG was shown to be more effective in exercising an inhibitory activity even at low concentration. On the other hand, the growth inhibitory activity of ONPG increase in dramatically in the presence of 3.5mM IPTG as an inducer