Hurwitz, Charles (Veterans Administration Hospital, Albany, N.Y.) and Carmen L. Rosano. Accumulation of label from C(14)-streptomycin by Escherichia coli. J. Bacteriol. 83:1193-1201. 1962.-Accumulation of label from C(14)-streptomycin by sensitive Escherichia coli occurs in the presence of chloramphenicol, provided the cells receive a prior exposure to streptomycin. The rate of accumulation increases with the concentration and length of exposure to streptomycin during the initiation phase. Accumulation of label from streptomycin in the presence of chloramphenicol is also a function of the streptomycin concentration during the killing phase. Evidence is presented for the presence of a barrier to the entry and exit of streptomycin. It is further shown that total accumulation of streptomycin can be divided into three portions: surface-adsorbed streptomycin, streptomycin present at the time of onset of loss of viability, and streptomycin accumulated by killed cells. Only about 10% of the total accumulated streptomycin is present at the onset of loss of viability and can therefore be presumed to play a role in the lethal action of the antibiotic.

Anti-Bacterial Agents↗

PubMed1962

Chloramphenicol-sensitive and-insensitive phases of the lethal action of streptomycin.

Hurwitz, Charles (Veterans Administration Hospital, Albany, N.Y.) and Carmen L. Rosano. Chloramphenicol-sensitive and -insensitive phases of the lethal action of streptomycin. J. Bacteriol. 83:1202-1209. 1962.-If chloramphenicol is added to sensitive Escherichia coli cells at the same time as streptomycin, the lethal effect of the latter drug is prevented. If the cells receive a prior exposure to streptomycin before the addition of chloramphenicol, the bacteria are then susceptible to killing by streptomycin in the presence of chloramphenicol. These results are interpreted to mean that the lethal action of streptomycin can be divided into chloramphenicol-sensitive and chloramphenicol-insensitive stages. It is proposed that during the chloramphenicol-sensitive stage, a streptomycin-initiated protein synthesis occurs, and that this protein synthesis must precede the actual killing by streptomycin. Inorganic phosphate has no effect on the chloramphenicol-sensitive phase, but does prevent killing by streptomycin. Evidence is presented arguing against the formation of a leaky permeability barrier as being the primary cause of death of cells exposed to streptomycin.

Chloramphenicol↗

PubMed1962

Kinetics of loss of vibility of Escherichia coli exposed to streptomycin.

Hurwitz, C. (Veterans Administration Hospital, Albany, N.Y.), C. L. Rosano, and J. V. Landau. Kinetics of loss of viability of Escherichia coli exposed to streptomycin. J. Bacteriol. 83:1210-1216. 1962.-The first effect of streptomycin on Escherichia coli B cells growing in nutrient broth is a decrease or cessation (depending on the concentration of antibiotic) of the rate of increase of viable cells. After this apparent bacteriostasis, a rapid decline in viable count begins. The length of time before onset of decline of viability is a first order function of the concentration of streptomycin between 0.1 and 2.0 mug/ml. Above 2.0 mug/ml, the lag in onset of loss of viability approaches asymptotically a value greater than 2 min. The length of the lag in onset of loss of viability is interpreted to be a measure of the rate of synthesis of the postulated streptomycin-initiated protein required for the later lethal action of the drug. Measurements of the effect of streptomycin on the rate of synthesis of protein by E. coli B cells show an immediate effect on the rate of protein synthesis, corresponding to the apparent bacteriostasis; this is followed by a later decrease in the rate of synthesis, which corresponds in time with the decline in viability. Washing exponentially growing E. coli B cells by centrifugation and resuspension in fresh nutrient broth makes the cells more resistant to streptomycin. The lag before the onset of decline in viability is prolonged, and the inhibition of protein synthesis is likewise affected. The washing procedure has no effect on total protein synthesis (as measured by incorporation of C(14)-leucine). Since synthesis of beta-galactosidase is also delayed by the washing procedure, this effect is interpreted to mean that washing delays induced protein synthesis, but has no effect on the rate of total protein synthesis. In an accompanying communication (Hurwitz and Rosano, 1962a), evidence was presented in support of the thesis that a chloramphenicol-sensitive, streptomycin-initiated protein synthesis is a necessary precursor for the lethal action of streptomycin. If a streptomycin-initiated protein synthesis is a necessary precursor of the lethal action of streptomycin, the kinetics of loss of viability of growing cells should show delineated phases corresponding to both the initiation and killing phases described in the preceding report. Studies of the kinetics of loss of viability and of the kinetics of inhibition of protein synthesis resulting from exposure of Escherichia coli to streptomycin were therefore undertaken to examine further the validity of the above thesis. In another accompanying report, the kinetics of accumulation of radioisotopic label from C(14)-streptomycin will be discussed in a similar context (Hurwitz and Rosano, 1962b).

Anti-Bacterial Agents↗

PubMed1962