Changes in surface charge density on liposomes induced by Escherichia coli endotoxin.

Changes in surface charge density of liposomes induced by E. coli endotoxin were studied by microelectrophoresis. Endotoxin altered the surface charge of phosphatidylcholine liposomes from neutral to negative. The negative charge of the endotoxin-phosphatidylcholine complex was neutralized electrostatically by binding with Ca2+ (2 mM). Phosphatidylcholine liposomes were made positive by addition of the positively charged detergent, hexadecyltrimethylammonium chloride. Endotoxin made the positively charged liposomes less charged. On the other hand, phosphatidylserine liposomes which were negatively charged became less charged in the presence of high concentration of endotoxin (8 mg/ml). The endotoxin effect on phosphatidylserine liposomes was abolished by EDTA (1 mM) but potentiated by CaCl2 (0.1--2 mM). These results indicate that endotoxin interacts with liposomes both hydrophobically and electrostatically.     

A novel ATP-driven glucose transport system in Escherichia coli.

In Escherichia coli wild-type cells and in ATPase-deficient cells (unc mutants), glucose was found to be transported mainly by an ATP-driven system. The evidence is based on experiments involving interference at different sites of energy metabolism with the use of uncouplers, arsenate, and starved cells. Furthermore, addition of succinate to starved cells increased glucose uptake only in the wild-type cells, where ATP could be regenerated. Glucose transport was also ATP-dependent in cells deficient in methyl-beta-galactoside transport (a system that carries glucose specificity). It was found to be shock-sensitive in all strains tested. The NOVEL ATP-driven glucose transport is a high-affinity (Km 3-10 microM) and high-capacity (V 240-330 Mmol . min-1 . mg cell protein-1) uptake system.     

Control of endotoxin release in Escherichia coli fed-batch cultures

High amounts of outer membrane (OM) components were released in glucose-limited fed-batch (GLFB) cultures at 37 °C at specific growth rates approaching 0.05 h⁻¹. Endotoxin analyses from a 20 °C GLFB culture gave similar results. An alternative fermentation technique, the temperature-limited fed-batch (TLFB) technique, reduced the endotoxin concentration in a culture with a biomass concentration of 30 g l⁻¹ from the 850 mg l⁻¹ in traditional GLFB cultures to about 20 mg l⁻¹. The TLFB technique uses the temperature to regulate the dissolved oxygen tension, while all substrate components are unregulated. It appears to be severe glucose limitation that triggers the extensive release of endotoxins rather than a low growth rate. Furthermore, it is not the low temperature that stabilizes the OM when using the TLFB technique. Simulations and experimental data show that this technique results in the same biomass productivity as the GLFB technique.     

Valproic acid disposition in rabbits during chronic treatment with Escherichia coli endotoxin

The disposition of valproic acid (VPA) in rabbits was studied after chronic treatment with Escherichia coli endotoxin. Endotoxin (1-2 micrograms/kg) was administered daily to 10 male New Zealand white rabbits for 5 days. On day 5, 50 mg/kg of VPA was given iv during the time of the peak febrile response. Blood samples were drawn at appropriate time intervals and analyzed for free and total VPA levels as well as plasma proteins and free fatty acids. The data were compared with similar control experiments performed 2 weeks before and after endotoxin treatment. Pharmacokinetic analysis indicated that the changes in free VPA clearance after endotoxin were related to the change in the febrile response during chronic treatment (r = 0.77; p less than 0.05); that is, animals which developed tolerance to the febrile response showed elevated drug clearance, whereas nontolerant animals showed decreased clearance of VPA.     

Evaluation of the MicroFoss system for enumeration of total viable count, Escherichia coli and coliforms in ground beef

This study was conducted to evaluate the performance of the MicroFoss system (Biosys, Ann Arbor, MI) for enumeration of total viable organisms, Escherichia coli and coliforms in ground beef. The system performance was compared to that of the USDA Bacteriological Analytical Method (BAM) reference culture methods. The correlation coefficients for the regression lines comparing the MicroFoss system detection times to the results of plate count methods for the total viable counts, coliform counts and the most probable number (MPN) method for E. coli were -0.95, -0.96 and -0.97, respectively. Tests comparing the reproducibility of data generated independently by two technicians on the same batch of samples showed no significant differences (P>0.05) in the MicroFoss detection times and culture results. The plate count methods for the total viable counts and coliform counts, and the MPN method for E. coli required 10, 11 and 22 times, respectively, the amount of time to complete tests compared to the length of time required to perform these tests using the MicroFoss system. The MicroFoss system produced reproducible data and provided a rapid and cost-efficient alternative method for enumeration of TVC, coliforms and E. coli in ground beef.     

uhp-directed, glucose 6-phosphate membrane receptor in Escherichia coli.

Membrane vesicles were characterized for their ability to specifically bind [14C]glucose 6-phosphate. Membranes prepared from a strain carrying a ColE1 uhp hybrid plasmid showed significantly enhanced glucose 6-phosphate binding. It is hypothesized that glucose 6-phosphate binding to these membranes is due to a uhpR-directed, membrane-bound receptor which functions in regulation of the inducible uhpT gene product: the hexose phosphate permease.