Rapid antibiotic susceptibility testing via electrochemical measurement of ferricyanide reduction by Escherichia coli and Clostridium sporogenes

Electrochemical measurement of respiratory chain activity allows rapid and reliable screening for antibiotic susceptibility in microorganisms. Chronoamperometry and chronocoulometry of suspensions of aerobically cultivated E. coli combined with the non-native oxidant potassium hexacyanoferrate(III) (ferricyanide) yield signals for reoxidation of the reduction product ferrocyanide that are much smaller if the E. coli has been incubated briefly with an effective antibiotic compound. Chronocoulometric results, obtained following 20-min incubation with antibiotic and 2-min measurement in assay buffer containing 50 mM ferricyanide and 10 mM succinate, at +0.50 V vs Ag/AgCl at a Pt working electrode, were compared with traditional disk diffusion susceptibility testing, which requires overnight incubation on agar plates; the results show significantly lower accumulation of ferrocyanide in all cases in which growth inhibition was observed in the disk diffusion assay. A range of antibiotic compounds (13) were examined that possess different mechanisms of action. Quantitative determination of IC50 values for penicillin G and chloramphenicol yielded values that were 100-fold higher than those obtained by standard turbidity methods after 10-h incubation; this is likely a result of the very brief (10 min) exposure time to the antibiotics. Addition of 5 microM 2,6-dichlorophenolindophenol, a hydrophobic electron-transfer mediator, to the assay mixture allowed susceptibility testing of a Gram-positive obligate anaerobe, Clostridium sporogenes. This rapid new assay will facilitate clinical susceptibility testing, allowing appropriate treatment virtually as soon as a clinical isolate can be obtained.     

连接器几何形态提高光导纤维的耦合性能

包围光纤的连接器套筒的设计对保持系统光学损耗处于低水平起着关键作用。     

Mucosal competitive exclusion to reduce Salmonella in swine

A mucosal competitive exclusion culture has been shown to reduce or eliminate Salmonella spp. in poultry. Using similar techniques, a mucosal competitive exclusion culture from swine (MCES) was produced from the cecum of a 6-week-old pig. Suckling pigs were inoculated with 5 ml of MCES by oral gavage within 6 h postfarrowing (PF) and again at 24 h PE All pigs were challenged with 10(3) CFU of Salmonella Choleraesuis at 48 h PF by intranasal instillation, including pigs from two sows that had not been given MCES. Clinical signs and rectal swabs were monitored daily, and pigs were allowed to suckle throughout the experiment. All pigs underwent necropsy on day 7 PF, and presence of Salmonella was determined in both qualitative (10 tissues) and quantitative (two tissues) samples. Clinical signs were inapparent in all pigs throughout the experiment. Recovery of Salmonella from rectal swabs was variable. However, 28% of the gut tissues were positive from the MCES-treated pigs versus 79% from the control pigs. A 2- to 5-log10 reduction of Salmonella in the cecal contents or ileocolic junction was observed in the MCES-treated pigs when compared with the controls. These data indicate that use of MCES may be a useful approach for control of Salmonella.     

钛合金弹簧

根据1986年在布里斯托尔召开的国际金属学会议上发表的论文“钛合金伴设计”报导,β型钛合金做为弹簧材料具有独特的综合性能。     

Effects of Ce on the short-term biocompatibility of Ti–Fe–Mo–Mn–Nb–Zr alloy for dental materials

Effects of Ce on the short-term biocompatibility of Ti-Fe-Mo-Mn-Nb-Zr alloy designed for implant materials were studied by acute toxicity test, hemolytic test, and MTT assay. The elements and their concentration in surface films and extraction media of Ti alloys were investigated with XPS and ICP, respectively. The primary compositions of the surface films of Ti alloys with 0.3% Ce and without Ce were TiO2 and Nb2O5. There were 0.2 mg/l Fe and 0.16 mg/l Mn in the extraction medium of Ti alloy without Ce, while 0.27 mg/l Fe and 0.87 mg/l Mn in the extraction medium of Ti alloy with 0.3% Ce. The concentrations of Fe and Mn in the medium were too low to have any significant effects on human health. There was no sign of cytotoxicity in these tests. The cytotoxicity levels of Ti alloys without Ce and with 0.3% Ce were graded 0 and 1, respectively. The hemolytic degrees of Ti alloys without Ce and with 0.3% Ce were 0.558% and 0.67%, respectively. The cells being incubated in the extraction medium were normal. These phenomena indicated that Ce was innocuous within the concentration range of this study. In addition, the hemolytic ratio and toxicity level of Ti alloy with 0.3% Ce were a little higher than that of Ti alloy without Ce. This meant that Ce would slightly increase the toxicity of Ti alloy.     

Radiation characteristics of a high-emissivity cylindrical-spherical cavity with obscuration

We have calculated, to first order, the apparent emissivity of the bounding diffuse surfaces of a high-emissivity cylindrical-spherical cavity enclosure. Our calculations indicate that to achieve emissivities close to a perfectly absorbing blackbody cavity along the bounding surfaces of the spherical enclosure, the radius of the sphere must be equal to or greater than a factor of 4 times the cylinder radius R(S) > or = 4R(C). Furthermore, to achieve emissivities approaching a blackbody cavity along the lower bounding surfaces of the cylindrical enclosure, the length of the cylinder must be a factor of 4 times greater than the radius of the cylinder L > or = 4R(C). In addition, we present the mathematical framework necessary to calculate radiant transfer within a cavity enclosure that contains obscuration. These results can be applied to the design of high-emissivity blackbody calibration cavities and to the reduction of stray light in terrestrial and spaceborne optical systems.     

Relative quantitation of intact proteins of bacterial cell extracts using coextracted proteins as internal standards

A method for quantitating protein expression using LC/MS of whole proteins is described. This method is based on the fact that some proteins present in cells are abundant universal proteins whose expression levels exhibit little variation. This method demonstrates that these coextracted proteins can be used as internal standards to which the other proteins in the sample can be compared. By comparing the intensities of a selected protein to marker proteins, or internal standards, a relative ratio is obtained. This ratio can then be used to determine the relative amount of protein expression between cellular extracts. The validity of this approach is described for a standard protein mixture, as well as, E. coli cells that were known to differentially express green fluorescent protein.     

Investigation of the inhibitory effect of silica on the degradation of 1,1,1-trichloroethane by granular iron

Although iron-based permeable reactive barriers are gaining importance for treating groundwater contaminants, little is currently known about the effect of cosolutes on barrier longevity. Because of their corrosion inhibiting properties, dissolved silica species are of particular concern. This research investigates the effect of silica on the reduction of 1,1,1-trichloroethane by granular iron as a function of added silica concentration, pH, and duration of iron exposure to dissolved silica. Batch studies reveal that, at pH 8.5 and above, added silica concentrations as low as 0.17 mM cause a 30% reduction in the reactivity of iron. At higher silica concentrations, reactivity decreases by 65-75%. The inhibitory effect is greater at higher pH: 0.83 mM silica has no apparent adverse effect at pH 7.5, but leads to a 46% decrease in reaction rate at pH 8 and 90% at pH 9. This corresponds to observed trends in silica adsorption onto iron, which is low at pH 7.3 but increases at higher pH. Extending the duration of iron exposure to silica solutions also leads to a more pronounced inhibitory effect. This is in good agreement with the increase in silica coverage on the iron surface as revealed by X-ray photoelectron spectroscopy.     

Reduction of poliovirus 1, bacteriophages,Salmonella montevideo,and Escherichia coli O157:H7 on strawberries by physical and disinfectant washes

The efficacy levels of different physical and chemical washing treatments in the reduction of viral and bacterial pathogens from inoculated strawberries were evaluated. Escherichia coli O157:H7, Salmonella Montevideo, poliovirus 1, and the bacteriophages PRD1, phiX174, and MS2 were used as model and surrogate organisms. Chemicals readily available to producers and/or consumers were evaluated as antimicrobial additives for the production of washes. The gentle agitation of contaminated strawberries in water for 2 min led to reductions in microbial populations ranging from 41 to 79% and from 62 to 90% at water temperatures of 22 and 43 degrees C, respectively. Significant reductions (> 98%) in numbers of bacteria and viruses were obtained with sodium hypochlorite (50 to 300 ppm of free chlorine), Oxine or Carnebon (200 ppm of product generating "stabilized chlorine dioxide"), Tsunami (100 ppm of peroxyacetic acid), and Alcide (100 or 200 ppm of acidified sodium chlorite) washes. Overall, 200 ppm of acidified sodium chlorite produced the greatest reductions of microorganisms. Hydrogen peroxide (0.5%) was slightly less effective than free chlorine in a strawberry wash and caused slight fruit discoloration. Cetylpyridinium chloride (0.1%) was effective in the reduction of bacterial species, while trisodium phosphate (1%) was effective against viruses. The consumer-oriented produce wash Fit was very effective (> 99%) in reducing the numbers of bacteria but not in reducing the numbers of viruses. Another wash, Healthy Harvest, was significantly less effective than Fit in reducing bacterial pathogens but more effective for viruses. The performance of automatic dishwashing detergent was similar to that of Healthy Harvest and significantly better than that of liquid dishwashing detergent. Solutions containing table salt (2% NaCl) or vinegar (10%) reduced the numbers of bacteria by about 90%, whereas only the vinegar wash reduced the numbers of viruses significantly (ca. 95%).