Howard S. Carr

Studies with hydroxyurea: I. The reversible inhibition of bacterial DNA synthesis and the effect of hydroxyurea on the bactericidal action of streptomycin

Abstract 1. Hydroxyurea is bacteriostatic for Escherichia coli. 2. Concentrations of hydroxyurea, which do not affect the synthesis and metabolism of RNA and proteins, induce a reversible inhibition of DNA synthesis. 3. The ribosomes, ribosomal RNA and messenger RNA from cells treated with hydroxyurea appear to be normal and functional. 4. The DNA from hydroxyurea-treated cells is not degraded nor does it appear to be cross-linked. 5. The mode of action of hydroxyurea appears to be different from that of compounds that irreversibly inhibit the synthesis of bacterial DNA. 6. Using hydroxyurea to inhibit the synthesis of DNA in E. coli, it could be shown that DNA synthesis is not required for the bactericidal effect of streptomycin.

Silver Sulfadiazine: Effect on the Ultrastructure of Pseudomonas aeruginosa

Pseudomonas aeruginosa exposed to silver sulfadiazine (AgSu) were examined in an electron microscope. The treated cells were distorted in shape, and structures (blebs) protruded from the cell surface. These “blebs” appeared to arise from the cell wall. A strain of P. aeruginosa resistant to AgSu did not display these changes. Upon exposure of P. aeruginosa to silver nitrate, none of these changes was seen; rather, such cells are characterized by large, central aggregations of nuclear material. The results are consistent with previous findings which suggested that AgSu acted at the cell surface. Images

Studies with hydroxyurea: VIII. The deoxyribonucleic acid of hydroxyurea-treated cells

Abstract 1. 1. The deoxyribonucleic acid isolated from bacteria devitalized by hydroxyurea is modified structurally. In spite of this modification the DNA can act as a primer for DNA-polymerase. The alteration of cellular DNA requires the metabolic participation of the bacterium. 2. 2. The DNA-synthesizing enzymes of hydroxyurea-treated bacteria appear to be intact and functional. 3. 3. A double-labelling procedure for analysing a mixture of DNAs derived from normal and from treated cells is introduced. It takes advantage of the ability of ECTEOLA-cellulose to discriminate among DNA molecules on the basis of size and configuration. 4. 4. The rapid and facile isolation of a DNA-synthesizing system from embryonic chicks is described. This system has an absolute requirement for single-stranded DNA primer.

Studies with hydroxyurea VI. Effects of hydroxyurea on the metabolism of sensitive and resistant strains of Escherichia coli

Abstract The effects of hydroxyurea on the metabolism of a sensitive and resistant strain of Escherichia coli were investigated. In sensitive bacteria the drug inhibits DNA synthesis and especially the incorporation of adenosine, deoxyadenosine and cytidine into DNA. Resistant bacteria are much less sensitive to the lethal action of hydroxyurea, however, the drug does exert a bacteriostatic effect. Such cells are also capable of incorporating thymidine into DNA in the presence of the drug. The evidence indicates that nucleotide reductase(s) is not the enzyme affected by hydroxyurea in E. coli C600. Bacteria resistant to hydroxyurea are as sensitive to the related compound hydroxyurethane as the parent strain from which they were derived.

Silver Sulfadiazine: Effect on the Growth and Ultrastructure of Staphylococci

Clinical isolates of Staphylococcus aureus and S. epidermidis were sensitive to levels of silver sulfadiazine (AgSu) that can readily be achieved topically. As a

Unusual growth properties of a bacterial strain lacking DNA polymerase

Summary The DNA polymerase-deficient E . coli strain pol A1− exhibits a 5% plating efficiency when grown on synthetic liquid medium and plated on a nutritionally rich solid medium. This phenomenon is not seen when the composition of the liquid and solid media is identical. Accordingly in order to obtain meaningful results with this strain, the growth conditions must be controlled carefully.

“Reversion” of DNA polymerase-deficient Escherichia coli

SummaryWhen a DNA polymerase-deficient strain of E. coli (pol A- mutant; amber nonsense) was exposed to methyl methanesulfonate or to nitrosomethylurethan, drug-resistant mutants which had recovered the pol A+ character were isolated. On the other hand, exposure of pol A- bacteria to nalidixic acid or to streptozotocin resulted in the recovery of mutants with specific resistance only to nalidixic acid or streptozotocin. These mutants retained the pol A- character.

DNA damage produced by povidone-iodine in cultured human diploid cells.

Povidone-iodine is capable of selective altering the DNA of human diploid cells growing in culture. This finding extends to eukaryotic cells, the previously reported DNA-modifying activity of this agent for bacteria. In view of the known relationship between DNA-modifying activity and potential carcinogenicity, the results suggest that the potential hazards posed by the widespread use of this agent be evaluated.

R Factor in Enterobacter cloacae Resistant to Silver Sulfadiazine

A strain of Enterobacter cloacae resistant to silver sulfadiazine was recovered from a unit in which this antimicrobial agent was in use. This strain was found to harbor an R factor responsible for resistance to carbenicillin, kanamycin and ampicillin. These antibiotic resistances were transferable to Escherichia coli by mating. Resistance to silver sulfadiazine was not, however, transmissible.

Studies with hydroxyurea: The biologic and metabolic properties of formamidoxime

Abstract Formamidoxime is a preferential inhibitor of bacterial and mammalian DNA synthesis. In bacteria, levels of formamidoxime up to 0.05 M are bacteriostatic while concentrations in excess of 0.05 M cause bacterial death. This lethal effect is accompanied by degradation of the cellular DNA. Inhibitors of protein and RNA synthesis and blockers of energy metabolism prevent formamidoxime-induced death. The two inhibitory effects of the chemical, viz. lethality and inhibition of DNA synthesis, are separable. A bacterial mutant deficient in DNA polymerase was much more sensitive to the lethal action of formamidoxime than its parent. The inhibitory effect of formamidoxime appears to be the result of its structural relationship to hydroxyurea.