Antibiotic activity of tigecycline against clinical pathogens by the micro dilution method

Resistant pathogens are the cause of clinical infections which threatening the patients lives and challenging the health systems through their economic importance. Therefore, new antibacterial agents with a broader spectrum of activity that protect against development of resistance are required. Tigecycline (Tygacil, Wyeth) is a relatively new FDA and EMEA approved glycylcycline antimicrobial with an expanded broad-spectrum activity against pathogens involved in complicated skin and skin structure infections. In this study we evaluated the in vitro activity of tigecycline in comparison to 14 other antibiotics against 182 clinical pathogens by use of the micro dilution method. In overall, tigecycline exhibited the lowest Minimum Inhibitory Concentration (MIC) values in almost all bacteria with a mean of 0.52 ± 1.25 mg/L, followed by meropenem and levofloxacin (mean MIC values 1.29 ± 2.52 and 1.45 ± 3.078 mg/L, respectively). MIC50 and MIC90 values of tigecycline were: 0.06 and 0.15 mg/L for E. coli, 0.12 and 1.00 mg/L for Klebsiella sp., 0.12 and 0.85 mg/L for various Enterobacter sp., 1.00 and 8.00 mg/L for Pseudomonas sp., 0.25 and 1.00 mg/L for Acinetobacter sp., 0.06 and 0.12 mg/L for Serratia sp., 0.12 and 0.25 mg/L for Staphylococcus aureus, 0.5 and 5.00 mg/L for Streptococcus sp. The MIC values recorded were among the lowest in recent literature for Acinetobacter sp. (included A. baumannii), and comparable to those obtained for Klebsiella, Serratia and Enterobacter indicating that tigecycline has a promising in vitro activity.     

超广谱β-内酰胺酶细菌检测方法及与耐药质粒关系研究

目的：建立一种准确、快速、低廉的检测超广谱β-内酰胺酶（ESBL）细菌方法。方法：以克拉维酸为ESBL的抑制剂、3种第三代头孢菌素（TGC）和氨曲南为底物、某些药敏结果为补充,建立了多底物协同方法,并与E-test方法进行了对照,符合率80%,不符合菌株用质粒提取、细菌转化、接合传递试验进行验证。结果：对116株疑产ESBL细菌用多底物协同方法和E-test方向同时检测,前者比后者阳性率高。结论：该方法准确、快速、价格低廉,特别适于常规应用。     

结核分枝杆菌对异烟肼耐药的分子机制

抗结核一线药物异烟肼是应用最广泛的抗结核药物之一,自1952年应用于临床以来,异烟肼就成了治疗结核和潜在感染的基础药物.有报道,我国异烟肼耐药已排在首位.结核分枝杆菌对异烟肼耐药的分子机制十分复杂,涉及katG、inhA、kasA、ndh、axyR等多种基因,本研究仅就此方面的研究作一综述.     

Starch modification by iterated syneresis

Potato, tapioca, corn and wheat starches were solubilised in water and isolated from the solution by iterated syneresis and the effect of this physical modification on the physicochemical properties and structure was studied. The experimental starches were examined by chemical analysis, the Brabender rheological method, scanning electron or light microscopy, X-ray diffractometry, infrared spectroscopy, and differential scanning calorimetry. Physical modification was evidenced to the change starch–water interaction and the structure of starches. Pasting temperature shifted to lower values and the gelatinisation mechanism changed. All modified starches had a B-type of X-ray diffraction pattern. The melting temperature of starch crystallites was typical of retrograded starch, but the enthalpy change was higher. The correlation between the resistant starch content of modified starches and their crystal structure was discussed together with the thermal properties.     

Selection and characterization of ethionine-resistant alfalfa (Medicago sativa L.) cell lines

Summary Diploid alfalfa (HG2), capable of plant regeneration from tissue culture, was used to select variant cell lines resistant to growth inhibition due to ethionine (an analog of methionine). Approximately 10⁷ suspension-cultured cells were mutagenized with methane sulfonic acid ethylester and then plated in solid media containing ethionine. Callus colonies formed on media with 0.02 mM ethionine. Of the 124 cell lines recovered, 91 regenerated plants. After six months growth on media without ethionine, 15 of 110 cell lines of callus grew significantly better than HG2 on 1 mM ethionine. Several ethionine-resistant callus cultures were also resistant to growth inhibition due to the addition of lysine + threonine to the media. High concentrations, relative to unselected HG2 callus, of methionine, cysteine, cystathionine, and glutathione were found in some, but not all, ethionine-resistant callus cultures. Cell line R32, which had a ca. tenfold increase in soluble methionine, had a 43% increase in total free amino acids and a 40% increase in amino acids in protein as compared to unselected HG2 callus. Relative amounts of each amino acid in protein were the same in both.Abbreviation LT lysine + threonine in equimolar concentration     

The coexistence of Escherichia coli serotype O157:H7 and its specific bacteriophage in continuous culture

For the development of phage therapy, systematic understanding mechanisms of bacteriophage resistance will be required. We describe a new strain of Escherichia coli O157:H7, named Mu(L), which stably co-exists with the O157:H7-specific lytic bacteriophage PP01. Chemostat cultures of E. coli O157:H7 infected with PP01 showed unchanging cell concentration, but phage concentrations which increased by approximately 10(8) PFU mL(-1). However, the latent period, burst size, and growth rate of Mu(L) were the same as in a PP01-susceptible strain. The binding rate of PP01 to the cell surface was diminished 8.5-fold in Mu(L). By observation of the binding of fluorescently labeled O157:H7-specific phage to individual Mu(L) cells, we found that clonal Mu(L) cultures were heterogeneous in their ability to bind bacteriophage. 15% of the Mu(L) population was completely resistant to PP01 infection. Mu(L) also co-existed with bacteriophages unrelated to PP01. Broad-range phage resistance by clonal heterogeneity represents a new class of bacteria-phage interactions.     

Plasmodium berghei: uptake of clindamycin and its metabolites by mouse erythrocytes with clindamycin-sensitive and clindamycin-resistant parasites.

Tritiated Clindamycin was used to compare the uptake of Clindamycin in plasma and red cells of mice infected with clindamycin-sensitive or clindamycin-resistant Plasmodium berghei and in uninfected mice. Red cells infected with either sensitive or resistant parasites have a higher concentration of [³H]clindamycin and its active metabolites 1 hr after drug administration than uninfected red blood cells. There was no significant difference in uptake of Clindamycin by red blood cells parasitized by sensitive or resistant parasites. Levels of Clindamycin and its metabolites were consistently higher in red cells than in plasma, both in infected and uninfected mice, but the drug was readily removed by washing red cells with phosphate buffered saline in either case. It is concluded that resistance to Clindamycin is not due to an impaired uptake of the drug by the parasitized red cell as has been shown for chloroquine resistance in P. falciparum and P. berghei.     

草原植物的放牧抗性

放牧抗性是指在放牧系统中,草原植物生存和生长的相对能力,包括避食性和耐牧性两部分,放牧避食性是指植物降低被牧食的机率和强度等机制,而耐牧性是指植物被牧食以后刺激植物再生长的机制,对物种抗性阈值和耐牧性阈值的研究将有利于解释放牧演替理论的原因和机制,不同的物种其抗性阈值和耐牧性阈值不同,这主要起决于它们放牧抗性策略,在草地管理中,认识植物将避食性和／或耐牧性机制作为诱导物种组成变化的优先抗性策略具有重要的理论和实践意义。