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1.
R factors of compatibility group A 总被引:4,自引:0,他引:4
2.
Faecal samples were taken weekly from a chosen pen on each of four commercial pig farms, two of which used olaquindox as a feed additive. Coliform bacteria were isolated from the samples and the incidence and level of resistance to olaquindox and to four therapeutic antibiotics determined. The coliforms isolated were biotyped to follow the emergence of drug-resistant sub-populations. The results showed that the coliform flora was complex and that a turnover of biotypes was associated with changes in the occupancy of the pen and, possibly, diet. This turnover led to large fluctuations in both incidence and level of resistance to olaquindox and the antibiotics. Olaquindox resistance was not specifically linked with resistance to any therapeutic antibiotic, and the possible origin of olaquindox-resistant strains is discussed in relation to the biotypes. 相似文献
3.
G Harris A Holmes S A Sabovljev W A Cramp M Hedges S Hornsey J M Hornsey G C Bennett 《International journal of radiation biology and related studies in physics, chemistry, and medicine》1986,50(4):685-694
The proliferation of human blood lymphocytes from ageing donors, responding to concanavalin A, showed greater sensitivity to inhibition by X-rays than similar cells from younger donors. This increased sensitivity was associated with deficiency in repair of X-ray-induced damage to nuclear material, as measured by density in sucrose gradients, and with increased incidence of chromosomal damage following exposure of freshly isolated lymphocytes. There was also an increased frequency of spontaneous chromosomal aberrations in ageing subjects whose lymphocytes were deficient in repair of DNA damage. 相似文献
4.
IncH1 plasmids and the F plasmid of Escherichia coli display one-way compatibility. An entering IncH1 plasmid is incompatible with a resident F plasmid, but is compatible when it is the resident plasmid. There is little molecular homology between IncH1 plasmids and the F plasmid. A single 5 MDal EcoRI restriction enzyme fragment from digests of several IncH1 plasmids hybridizes with probes constructed from the primary replication region of F. Homology can be demonstrated only with the gene for the essential replication protein of F (gene E), but the expression of incompatibility behaviour appears to be associated with the presence of the secondary replicon of the F plasmid. Thus R27 and F are compatible under growth conditions allowing replication and maintenance of F by the secondary replicon. However, a mutant F plasmid which lacks the secondary replicon of F is incompatible with R27 in both directions, irrespective of the growth conditions used. 相似文献
5.
E. Messens A. Lenaerts M. Van Montagu R. W. Hedges 《Molecular & general genetics : MGG》1985,199(2):344-348
Summary Plant cells neoplastically transformed by insertion of T-DNA from Ti plasmids of agrobacteria produce and secrete opines. Secretion of two of these opines (octopine and nopaline) is shown to require the expression of a single gene, which we designate ons.Dedicated to Professor Georg Melchers to celebrate his 50-year association with the journal 相似文献
6.
Dynamic changes in the Escherichia coli population in the calf gut were studied over 21 days in a group of 18 intensively-reared market calves. Isolates were identified by O-serogrouping, biotyping and resistogram patterns. Seventy O-serogroups were identified among nearly 3000 E. coli isolates examined and these were subdivided into 416 strains by means of their biotype and resistogram. Seventy-five per cent of these strains were detected only once or twice, which points to the continual replacement of the E. coli flora with strains that showed low persistence in the gut. The rise in the frequency of antibiotic resistance observed during the study was not due to a change in the proportion of resistant to sensitive strains in the gut flora. It was a consequence of the displacement of the original flora by multiply-resistant strains, which presumably originated from the calves' environment. 相似文献
7.
Alterations in cell membrane structure and expression of a membrane-associated protein after adaptation to osmotic stress 总被引:3,自引:0,他引:3
8.
S. K. St. Martin K. S. Lewers R. G. Palmer B. R. Hedges 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,92(1):78-82
Methods for identifying germplasm carrying alleles with the potential to improve a particular single-cross hybrid have been proposed and discussed in recent years. There is a need for similar methods to be used in breeding crops for which pure-line cultivars, rather than hybrids, are the goal. The objective of this research was to develop a method to identify germplasm lines with the potential to contribute favorable alleles not present in a specified pure line or set of pure lines. Given a set of adapted pure lines (A
1, A
2 ..., A
m) to be improved and a set of germplasm lines (P
1
P
2 ..., P
f), the procedure consists of producing all f x m possible hybrids and evaluating them along with the parents. The testcross statistic T
ij is defined by T
ij=(F
ij–A
j)+(1–) (F
ij–P
i), where A
j, P
i, and F
ij represent the performance of thej
th adapted line, the i
th germplasm line, and their hybrid, respectively. The statistic
is the mean value of T
ij over all adapted parents A
j. If =(1/2)(1+d), where d = the mean degree of dominance, then T
ij measures the potential for alleles from P
i to improve A
j and
measures the potential for alleles from P
i to improve the set A
1, A
2 ..., A
m. Use of data on soybean and peanut hybrids published by other researchers suggests that the value assumed for d has little effect on the P
i chosen. The ability of the T
ij and
statistics to identify germplasm strains carrying rare favorable alleles should be assessed in empirical studies.Joint contribution: OARDC (Journal Articale No. 161-94), USDAARS, Iowa Agriculture and Home Economics Expriment Station (Journal Paper No. J-16109; Project 2985), and Agreculture and Agri-Food Canada. Salaries and research support for S. K. St. Martin Provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, Ohio State University 相似文献
9.
10.