The Action of Antibiotics on Indole Synthesis by Cell Suspensions of Escherichia coli

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Abstract
Washed suspensions of Escher-ichia coli strain 7-4 form indole from simple precursors, and this action can be inhibited by bacteriostatic concentrations of chlorampheni-col and the tetracyclines (Aureomycin, Terramycin, and Achromycin). The effect of these antibiotics does not seem to be due to inhibition of adaptive enzymes, since indole synthesis proceeding at a maximum rate can also be inhibited. Streptomycin inhibits indole synthesis only at higher than bacteriostatic concentrations. The synthesis of indole by suspensions of antibiotic-resistant organisms is much less susceptible to antibiotic action. There is a correlation between the amount of antibiotic required to inhibit indole synthesis and to inhibit growth. Results suggest that the antibiotics interfere with reactions associated with the synthesis of indole.