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Biomedical subjects

W Yan

Publications and source records attributed to W Yan.

179 records · Page 10Linked to original sources
PubMed1991

Characterization of erythromycin resistance in Campylobacter jejuni and Campylobacter coli.

The mechanism of resistance to erythromycin, the drug of choice in the treatment of campylobacter gastroenteritis, was investigated. Erythromycin resistance (MICs, greater than 1,024 micrograms/ml) in three clinical isolates of Campylobacter jejuni and one C. coli isolate was determined to be constitutive and chromosomally mediated. In vivo protein synthesis in erythromycin-susceptible C. jejuni and C. coli strains was completely inhibited by low levels of erythromycin (5 micrograms/ml), whereas a high concentration of the antibiotic (100 micrograms/ml) had no effect on protein synthesis in erythromycin-resistant strains. Biological assays showed that extracellular degradation of erythromycin was not responsible for erythromycin resistance in strains of Campylobacter species. The rates and amounts of uptake of [14C]erythromycin by resistant and susceptible campylobacter cells were determined to be similar. Binding assays with purified campylobacter 70S ribosomes as well as 50S ribosomal subunits showed that those from erythromycin-resistant strans bound much less [14C]erythromycin than did those from susceptible strains. Genomic DNA from C. coli UA585 was used to transform erythromycin resistance to C. coli UA417. The erythromycin resistance marker was associated with a 240-kb SmaI fragment of the C. coli UA585 genome. Our results rule out erythromycin inactivation or efflux and are not consistent with the production of an RNA methylase, although they are consistent with a mutational mechanism of resistance due to a change in a ribosomal protein gene. This study constitutes a detailed biochemical and genetic characterization of erythromycin resistance in Campylobacter species.

Bacterial Proteins↗
PubMed1991

[Cloning and orientation of a promoter of thermophilic Thiobacillus sp].

Thiobacillus sp. is an obligate autotrophic thermophilic bacterium which was isolated from an acidic hot spring in Yunnan Province. Its optimum growth temperature is 45-50 degrees C and its optimum pH is 2.0-3.0. Using DNA recombinant technique, we inserted the HindIII fragments of the Thiobacillus sp. chromosomal DNA into the HindIII site of promoter-probe plasmid pSDSI (AprTcs, 5.65 kb). Transformants resistant to tetracycline were obtained on Tc plates (12 micrograms/ml). Of these, twenty transformants were able to grow on 120 micrograms/ml Tc plates, and two of them, designated pSDH7 and pSDH11, were able to grow on plates containing Tc at concentration up to 360 micrograms/ml. With HindIII, pSDH11 produced a 0.95kb fragment which had the function of promoter and a PstI site besides the 5.65 kb fragment of pSDSI. Southern blot hybridization showed that the 0.95 kb insert was from the Thiobacillus sp. chromosomal DNA. After restriction mapping, a 2.85 kb fragment of pSDH11 (which contained 0.7 kb of the inserted fragment) was removed with the aid of Pst1, and the remained fragment was used to construct a 3.75 kb plasmid (named pSDH114) which was resistant to a higher level of tetracycline (360 micrograms/ml) than for pBR322 (120 micrograms/ml). The remained 0.25 kb foreign fragment in pSDH114 still retained full function of the promoter contained in the original 0.95 kb. Thus we could orient the cloned promotor function fragment (0.25 kb) from Thiobacillus sp. in pSDH114.

Cloning, Molecular↗
PubMed1991

Cmax/AUC is a clearer measure than Cmax for absorption rates in investigations of bioequivalence.

In bioequivalence studies, the maximum concentration (Cmax) is shown to reflect not only the rate but also the extent of absorption. Cmax is highly correlated with the area under the curve (AUC) contrasting blood concentration with time. Therefore, use of the Cmax/AUC ratio is recommended for assessing the equivalence of absorption rates. The ratio is independent of both intrasubject variations and possible differences in the extent of absorption and reflects only the contrast between the absorption and disposition rate constants (ka/k).

Absorption↗
PubMed1991

[Autologous bone marrow transplantation in acute myeloid leukemias: a report of 7 cases].

Seven patients with acute myeloid leukemias (AML) in complete remission (CR) were treated with high dose chemotherapy and/or total body irradiation (TBI) followed by autologous bone marrow transplantation (ABMT). The clinical status of the 7 cases at ABMT were as follows: 5 in CR1 (2 with standard risks and 3 with high risks) and 2 in CR2 (both with standard risks). The conditioning regimens used for ABMT were cyclophosphamide plus TBI in 3 cases, high dose busulfan plus cyclophosphamide in 3 cases, and BACT program chemotherapy in 1 case. All 7 cases showed hemopoietic reconstitution after ABMT; no death occurred within the post-transplantation aplasia period, but hepatotoxicity was observed with high dose busulfan. Up to December, 1989, 2 patients in CR1 with standard risk receiving transplants had survived, disease free, for 26 and 18 months, respectively; one of 2 patients in CR2 with standard risk receiving transplants had survived for 30 months, and the other died at the 9th month after ABMT with no sign of leukemia relapse. Two of the 3 patients with high risk relapsed at 5 months post-ABMT and the third was in continuous CR for 5.5 months.

Adult↗
PubMed1990

[Cloning and expression of a promoter function fragment from Thiobacillus thiooxidans in Escherichia coli].

This paper reports a recombinant plasmid pSDR12 which is constructed through the substitution of the EcoRI-HindIII fragment of pBR322 by a specific fragment of chromosomal DNA of T. thiooxidans. After it was transformed into C600, the transformants revealed higher levels of Tc resistance. This result shows that a promoter function fragment from autotrophic bacteria is able to express in Escherichia coil.

Acidithiobacillus thiooxidans↗
PubMed1989

Mapping of transfer and H pilus coding regions of the IncHII plasmid pHH1508a.

The IncHII plasmid pHH1508a (208 kilobases) encodes resistance to potassium tellurite, trimethoprim, and streptomycin. Conjugative pili encoded by pHH1508a were isolated, purified, and used for preparation of anti-H pilus antiserum. Immuno-gold labelling experiments using H pilus specific antiserum showed that antigenic determinants were located along the entire length of the H pilus. Immuno-gold labelling and lysis studies using pilH alpha, a bacteriophage specific for H pili, were used to investigate transfer-deficient mutants of pHH1508a obtained by Tn5 mutagenesis and an in vitro constructed derivative of 96 kilobases, pDT1178, which also conferred resistance to potassium tellurite, trimethoprim, and streptomycin. The transfer-deficient mutants did not specify H pili, whereas pDT1178, which transferred at low frequency (1 x 10(-4) transconjugants per recipient), specified a small number of H pili. A naturally occurring plasmid, pMG110, was found to encode the production of H pili, but was completely transfer deficient (less than 1 x 10(-7) transconjugants per recipient). This study suggests that genes required for H pilus production and assembly as well as low level transfer are located separately within the 96-kilobase fragment of pDT1178 and that other genes, located outside this region, are essential for the regulation and full expression of conjugative transfer.

Conjugation, Genetic↗
PubMed1988

Rabbit articular chondrocytes in soft agar are useful to test the effect of non-steroidal anti-inflammatory drugs on chondrocyte replication.

The effect of non-steroidal anti-inflammatory drugs (NSAIDs) on rabbit articular chondrocyte proliferation was examined in soft agar and in conventional cultures on plastic dishes. Indomethacin, acetylsalicylate, and naproxen (10(-4) M) decreased the efficiency of colony formation by chondrocytes in soft agar in the presence of fibroblast growth factor, although the drugs had little effect on the proliferation of chondrocytes on plastic dishes. On the other hand, tiaprofenic acid (10(-4) M) did not have any adverse effect on chondrocyte replication in either culture the two systems. Rabbit articular chondrocyte growth in soft agar will be a useful test system for examining the effects of anti-arthritic drugs on cartilage metabolism and repair.

Agar↗
PubMed1987

Characterization of transfer regions within the HII incompatibility group plasmid pHH1508a.

A circular map of the 208-kilobase IncHII plasmid pHH1508a was constructed by using the restriction endonucleases XbaI, XhoI, and NotI. Tn5 insertion mutagenesis showed that transfer genes were distributed widely over the plasmid map. Analysis of the deletion mutant pDT1178 indicated that genes required for conjugative pilus production are located in a 96.0-kilobase region of the plasmid.

Chromosome Mapping↗
PubMed1985

Mapping of transfer regions within incompatibility group HI plasmid R27.

Plasmids of incompatibility group HI are large (greater than 150 kilobases [kb]) and possess an unusual thermosensitive mode of conjugative transfer. R27, the prototype IncHi1 plasmid, encodes resistance to tetracycline via a determinant which is related to transposon Tn10. A restriction endonuclease map of R27 (size, 182 kb) was recently constructed with ApaI, PstI, and XbaI. Transfer genes within R27 were mapped by insertion of Tn5 and Tn7. At least two different regions of the plasmid were concerned with transfer functions. Insertions into either region completely abolished transfer. None of the insertions had any effect on entry exclusion (Eex) of other IncH plasmids. However, a deletion mutant which lacked the Eex function was obtained, allowing us to map the probable site of the gene encoding Eex to one of the two transfer regions. The tetracycline resistance determinant in R27 was located within an 8-kb region between the two main transfer regions. The transfer genes, therefore, are not located together in R27 but are situated in at least two major widely separated transfer regions.

Chromosome Mapping↗
PubMed1983

The study and clinical application of the osteocutaneous flap of fibula.

In this article, four cases of free fibular osteocutaneous flap transfer are reported. The advantages of the bone-attached flap, its microsurgical anatomy, and its design and method of isolation are discussed in detail. Postoperative follow-up showed success in all four cases with satisfactory functional recovery.

Accidents, Occupational↗
PubMed1979

Comparison of physiological responses to hypoxia at high altitudes between highlanders and lowlanders.

This report deals with the differences and changes of physiological functions of the highlanders and the lowlanders at different altitudes during the period when the Chinese Mountaineering Team was climbing up and reached the peak of Qomolangma Feng. In a period of relaxation, there are no significant changes in ventilatory responsiveness to hypercapnia, electrocardiogram and electroencephalogram between highlanders and lowlanders with the changes at different altitudes. At 5,000 m a.s.l., however, electrocardiogram and the result of cardiac ventricular functional test show significant differences after the subjects are physically loaded. Those whose electrocardiogram readings show unusual changes, and whose cardiac ventricular functional tests show their physiological functions at low degree after physical activities at the altitude of 5,000 m, have a climbing ability hardly below 6,500 m, while those who have reached the altitudes above 8,200 m have no unusual changes in electrocardiogram, and the results of cardiac ventricular functional tests show that their physiological functions are at high degree.

Acclimatization↗
PubMedDate not supplied

Genetic characterization of kanamycin resistance in Campylobacter coli.

The restriction map of plasmid pIP1433 from Campylobacter coli BM2509, isolated in France, was constructed and the location of the kanamycin (Km) and tetracycline (Tc) resistance markers determined using probes for aphA-3 and tetO genes, respectively. These DNA probes were used to study a second Km- and Tc-resistant strain C. coli UA696, isolated in Canada. In this strain, the Km resistance determinant was located in the chromosome. Like pIP1433, the Km resistance determinant in C. coli UA696 specified a 3'-aminoglycoside phosphotransferase of type III whereas the tetO gene was located on a non-transmissible plasmid.

Campylobacter↗
PubMedDate not supplied

[Relation of the snow cover to the structure of vegatation in the alpine communities of the eastern Tsinghai-Tibet Plateau].

The type of snow cover considerably influences the sctructure of vegetation and production-related processes in alpine communities of diverse regions. The relation of snow cover thickness to the structure of apline plant communities in the eastern Tsinghai-Tibet Plateau (Sichuan, People's Republic of China) was studied by analyzing the vegetation in 251 sample areas grouped in five transects along the gradient of mesotopographic conditions and wintertime snow cover thickness. Considerable differentiation of plant communities related to snow cover thickness in revealed along the line from the northern to the southern slope. It is shown that the influence of snow cover on the distribution of particular plant species is significantly greater than the influence of soil properties (pH, content of humus, total phosphorus, potassium, and ammonia nitrogen in the upper strata of soil). Among the 56 herbaceous plant species and 7 shrub species studied, 52 herbaceous and all the 7 shrub species showed significant (P < 0.05) correlation (positive or negative) to snow cover thickness. Snow cover thickness appeared also significantly correlated to a number of soil properties: soil thickness, content of water, total phosphorus, and humus. But, in contrast to the alpine communities of the Caucasus and the Alps, no considerable acidification of the soil under snowflakes, due to perpetual removal of cations by melt water, was observed.

Adaptation, Physiological↗