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The combined actions of chloramphenicol and of bactericidal antibody plus complement on Salmonella typhosa.

Quantitative determinations, employing turbidimetric growth assays, have been made of the inhibitory actions of choramphenicol, and of specific antibody plus complement, separately, and in combination. In experiments with the Ty2 strain of S. typhosa the combined activities of the two groups of reagents have been predicted, within 3 per cent, from the activities of the separate components, on the hypothesis of joint, independent action (additive inhibitions). A fourfold increase in resistance to chloramphenicol of the 0901 strain of S. typhosa has been shown to have little, if any, effect on its susceptibility to the bactericidal action of anti-O antibody and complement. Indirect evidence indicates that the latter may not be a general effect but may vary with the particular strain.

Anti-Bacterial Agents↗

The effect of chloramphenicol on deoxyribonucleic acid synthesis and the development of resistance to ultraviolet irradiation in E. coli infected with bacteriophage T2.

To elucidate the role of protein synthesis in DNA formation, E. coli R2 infected with phage T2 was studied as a model, employing chloramphenicol to inhibit protein synthesis. The following results were obtained. 1. Chloramphenicol inhibited protein synthesis but not synthesis of nucleic acids in uninfected bacteria. 2. Studies of the effect of chloramphenicol on phage maturation indicated a delay of 2 minutes between time of addition and cessation of phage growth. 3. The increase of DNA in phage-infected bacteria was completely suppressed by the addition of chloramphenicol within 2 minutes following infection. Addition at later times showed progressively less inhibitory action depending upon the time interval, and addition after the 10th or 12th minute showed no appreciable effect on DNA synthesis despite the cessation of intracellular phage formation and protein synthesis. 4. When chloramphenicol was added to infected cells the increase of resistance to UV stopped within 2 minutes, whether or not DNA synthesis continued. Thus evolution of resistance paralleled the rate of DNA synthesis achieved, but not the amount of DNA accumulated. 5. We conclude that in infected bacteria, protein synthesis is necessary to initiate DNA synthesis but is not essential for its continuation. The resistance to UV that characterizes infected cells near the midpoint of the latent period is not due to accumulation of DNA, but depends on some chloramphenicol-sensitive process (probably protein synthesis) completed at about the time the rate of DNA synthesis becomes maximal.

Bacteriophage T4↗