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Thermal chromatography of DNA-DNA reactions.

Genetic relationships among bacteriophages and bacteria have been investigated using an extension of the DNA-agar technique. Thermal elution profiles, each characteristic of a specific DNA-DNA reaction, have been obtained from reactions involving homologous and heterologous DNAs. A sizable portion of the DNA of lysogenic (or semilysogenic DNA) viruses has been shown to be homologous to the DNA of their bacterial hosts. These homologies are contained in numerous sequences throughout the viral DNAs. Furthermore, DNA homologies exist among most temperate phage DNAs as well as with their respective hosts.

Bacteriolysis↗

Analogy between temperature-dependent and concentration-dependent bacterial killing.

In this article an analogy between temperature-dependent and concentration-dependent bacterial killing is described. The validation process of autoclaves uses parameters such as reduction rate constant k, decimal reduction time D and resistance coefficient z from an imaginary microorganism to describe the sterilization process. Total lethality of the process is calculated as the integral of the lethality (a function of the temperature) over time. In the case of concentration-dependent killing-i.e. using antibiotic drugs-the k-value is not necessarily a constant; it is the difference between growth and killing of the microorganism. Equations are derived for the decimal reduction time D and resistance coefficient z. Pharmacodynamic models of tobramycin, ciprofloxacin and ceftazidime are used to demonstrate that there is an optimal concentration for all three drugs: C(opt-tobra)=3.20 MICmg/l, C(opt-cipro)=3.45 MICmg/l and C(opt-cefta)=1.35 MICmg/l.

Anti-Bacterial Agents↗

Scanning model for translational reinitiation in eubacteria.

Premature termination of translation in eubacteria, like Escherichia coli, often leads to reinitiation at nearby start codons. Restarts also occur in response to termination at the end of natural coding regions, where they serve to enforce translational coupling between adjacent cistrons. Here, we present a model in which the terminated but not released ribosome reaches neighboring initiation codons by lateral diffusion along the mRNA. The model is based on the finding that introduction of an additional start codon between the termination and the reinitiation site consistently obstructs ribosomes to reach the authentic restart site. Instead, the ribosome now begins protein synthesis at this newly introduced AUG codon. This ribosomal scanning-like movement is bidirectional, has a radius of action of more than 40 nucleotides in the model system used, and activates the first encountered restart site. The ribosomal reach in the upstream direction is less than in the downstream one, probably due to dislodging by elongating ribosomes. The proposed model has parallels with the scanning mechanism postulated for eukaryotic translational initiation and reinitiation.

Bacteriolysis↗

Granulocyte and granulocyte-macrophage colony-stimulating factors for treatment of neutropenia in glycogen storage disease type Ib.

Two children with glycogen storage disease type Ib associated with numerous recurrent bacterial infections as a result of neutropenia and neutrophil dysfunction were treated with recombinant human granulocyte colony-stimulating factor (G-CSF). One of the two patients was previously treated with recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF); therapy had to be discontinued because of severe local side effects. Both colony-stimulating factors at dosages of 3 and 8 micrograms/kg/per day, respectively, increased the average neutrophil counts from less than 300 cells/microliters to more than 1200 cells/microliters. Two subpopulations of neutrophils could be identified by their capacity to produce H2O2: one subpopulation generated H2O2 normally and a second was defective in H2O2 production. The doses of G-CSF effectively enhanced and maintained that subpopulation of neutrophils which produced normal amounts of H2O2. Moreover, these colony-stimulating factor-induced neutrophils demonstrated effective phagocytosis of zymosan particles and killing of staphylococci. Chemotaxis was decreased and could not be normalized by treatment with G-CSF. We conclude that maintenance treatment with G-CSF improved the quality of life in both patients: The number and severity of bacterial infections decreased markedly during treatment. Long-term treatment with G-CSF (12 and 10 months, respectively) was well tolerated, and no adverse clinical events were observed.

Adolescent↗

Selection for lysis inhibition in bacteriophage.

For Escherichia coli cells that have been infected by T-even bacteriophages (phages T2, T4, and T6), the adsorption of a second T-even phage results in an increase in the length of the original phage infection and an associated increase in the number of phages produced by the same infected cell. This is a phage encoded response called lysis inhibition. In this study the ecological significance of lysis inhibition is explored. In particular it is argued that lysis inhibition is an adaptive response to environments containing high concentrations of infected cells and low concentrations of uninfected cells.

Adsorption↗