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Biomedical subjects

E HAHN

Publications and source records attributed to E HAHN.

At least 37 records · Page 2Linked to original sources
PubMed1956

On the specificity of the desoxyribonucleic acid which induces streptomycin resistance in Hemophilus.

Streptomycin resistance of a high degree has been induced in sensitive populations of Hemophilus influenzae and Hemophilus parainfluenzae by desoxyribonucleic acids (DNA's) derived from streptomycin (SM)-resistant cells of at least one heterologous species of Hemophilus. The specificity of the DNA which controls SM resistance has been studied within and among species of Hemophilus by comparing, in a given population, the proportion of cells transformed to SM-resistant by DNA's derived from highly resistant cells of heterologous type or species with the proportion changed by the DNA derived from SM-resistant cells of the homologous type or species. The ratio resulting from this comparison correlates in general with the degree of kinship between recipient and donor cells suggested by accepted methods of bacteriologic classification. The numerical value of the ratio is much lower when the species of the recipient population and donor of the DNA differ than when they are of the same species. The data suggest that this ratio is of value as an index of degree of kinship of recipient and donor cells. Comparison of the activity of heterologous and homologous DNA's shows differences within species and degrees of differences among species not brought out by other available methods. The data suggest that H. influenzae is more closely related to H. parainfluenzae than to H. suis and that the relationship between H. parainfluenzae and H. suis is remote. Within the species H. influenzae and H. parainfluenzae the ratio of hetero-specific transformants to homospecific transformants appears to be relatively constant for a given recipient population. This ratio also appears to be independent of the type or group source of the heterologous species SM resistance DNA. The low proportion of cells in H. influenzae populations which are transformed to SM-resistant by DNA's derived from SM-resistant H. parainfluenzae and vice versa has been increased 4- to 15-fold by the replication of the heterologous species SM resistance DNA in the heterologous species. An alteration of the heterologous DNA by the host is suggested.

DNA↗
PubMed1954

Studies on the nature of hemophilus influenzae cells susceptible to heritable changes by desoxyribonucleic acids.

In E. influenzae the highly specific desoxyribonucleic acids (DNA's) which play the role of heredity determinants of type specificity and SM resistance, have induced these traits in only a small proportion of the population exposed to their action. The evidence suggests that this small proportion, "the susceptible cells" possess a property or substance needed by the DNA in order to induce an heritable change. The size of the small proportion of susceptible cells can be influenced significantly by a number of factors; when all the factors now to be listed are operating the frequency has not exceeded 1:1000. The Type of Origin of Recipient Cells.-Type a exhibits the lowest frequency, about 1:10,000,000, and type d the highest, approximately 1 per 1000 cells exposed. This type-specific property which controls the frequency of susceptible cells is an inherited trait; repeated change to a heterologous type shows no influence on the incidence of these cells. Concentration of DNA.-Within certain limits increase in the concentration of DNA controlling streptomycin resistance can increase the size of the proportion of cells in which streptomycin resistance can be induced. However, increases in concentrations greater than 10(-1) microg. per ml. have not induced streptomycin resistance in a higher proportion of cells. Phase of Growth Cycle.-Predictable fluctuations in frequency of induced heritable changes have been demonstrated in both Rb and Rd populations during growth. There is no evidence that susceptible cells reproduce their kind; they emerge in all experiments when the population reaches the end of the logarithmic period and a density of 2 to 4 x 10(8) cells per ml. In the early logarithmic phase it is difficult to demonstrate the presence of susceptible cells. The peak frequency of susceptible cells occurs in the early stationary phase of the growth cycle. Thereafter, the decline in frequency is a gradual one. The data suggest that in a given population the same cells are susceptible to a number of different type-specific DNA's and the DNA controlling SM resistance. Comparison of Frequency of Cells Susceptible to Different DNA's.-In a given population the frequency of cells susceptible to different type-specific DNA's and the DNA controlling streptomycin resistance is not significantly different. Competition between Type-Specific DNA's-The data suggest that DNA's of types a, b, and c compete for the same cells in Rd populations. When Rd populations are exposed simultaneously to 2 of these 3 DNA's in different concentrations the proportion which each type contributes to the total type-specific cells induced is closely correlated with the concentration of the corresponding DNA. Exclusion of DNA's.-Induction of one type specificity or streptomycin resistance can be completely prevented in a population containing susceptible cells by previous exposure for 15 minutes to a 1000-fold higher concentration of another type-specific DNA.

DNA↗
PubMed1953

In vitro production of new types of hemophilus influenzae.

Two new types of Hemophilus influenzae, Sab and Sad have been produced in vitro. Each exhibits the presence of the type specific polysaccharides of 2 types of E. influenzae within the same cell. In Sab the polysaccharides of types a and b have been demonstrated and in Sad those which characterize types a and d. The Sab and Sad traits are inherited. Sab was produced by the action of DNA-containing extract isolated from type a on either type b cells or Rb cells (non-encapsulated non-type-specific cells derived from type b). Sad cells were formed as a result of the action of the DNA-containing extract isolated from type d on cells intermediate between Rab and Sab cells. DNA-containing extracts isolated from Sab cells have induced the Sab trait in Rd cells with predictable regularity. Evidence has been presented that the hereditary determinant of Sab cells is a new genetic substance with new functions. Therefore, the interaction of the DNA-containing substance from cells of one genetic type with living cells of a genetically different type has produced what appears to be a new individual which differs from each of the cells contributing the differing genetic traits but has at least one trait in common with each. Sab cells derived presumably from a single cell show the appearance of type b cells sometime during the first 7 generations.

B-Lymphocytes↗