Enterobactin-Mediated Delivery of β-Lactam Antibiotics Enhances Antibacterial Activity against Pathogenic Escherichia coli

The design, synthesis, and characterization of enterobactin–antibiotic conjugates, hereafter Ent-Amp/Amx, where the β-lactam antibiotics ampicillin (Amp) and amoxicillin (Amx) are linked to a monofunctionalized enterobactin scaffold via a stable poly(ethylene glycol) linker are reported. Under conditions of iron limitation, these siderophore-modified antibiotics provide enhanced antibacterial activity against Escherichia coli strains, including uropathogenic E. coli CFT073 and UTI89, enterohemorrhagic E. coli O157:H7, and enterotoxigenic E. coli O78:H11, compared to the parent β-lactams. Studies with E. coli K-12 derivatives defective in ferric enterobactin transport reveal that the enhanced antibacterial activity observed for this strain requires the outer membrane ferric enterobactin transporter FepA. A remarkable 1000-fold decrease in minimum inhibitory concentration (MIC) value is observed for uropathogenic E. coli CFT073 relative to Amp/Amx, and time-kill kinetic studies demonstrate that Ent-Amp/Amx kill this strain more rapidly at 10-fold lower concentrations than the parent antibiotics. Moreover, Ent-Amp and Ent-Amx selectively kill E. coli CFT073 co-cultured with other bacterial species such as Staphylococcus aureus, and Ent-Amp exhibits low cytotoxicity against human T84 intestinal cells in both the apo and iron-bound forms. These studies demonstrate that the native enterobactin platform provides a means to effectively deliver antibacterial cargo across the outer membrane permeability barrier of Gram-negative pathogens utilizing enterobactin for iron acquisition.Pacific Southwest Regional Center of Excellence for Biodefense and Emerging Infectious DiseaseKinship Foundation. Searle Scholars ProgramMassachusetts Institute of Technology. Department of Chemistr

Physical properties of pectin aqueous solutions containing sunflower wax

The aim of this study is to investigate the physical properties of aqueous solutions of pectin (PA) containing sunflower wax (SFW), which are used as a basis for producing edible films. The stability and the rheological and microstructural characteristics of SFW/PA mixtures were evaluated. SFW/PA mixtures formed oil-in-water emulsions that were milky and opaque in appearance and were stable towards phase separation. Polarized micrographs revealed the presence of wax crystals, whose size decreased as pectin concentration increased. The rheological behavior of the aqueous solutions of pectin containing different amounts of SFW were best described by the generalized power law model of Herschel–Bulkley (H–B), which gave the best fit in all the range of shear rate values. Apparent viscosities and yield stress were determined using this model, and both properties increased with increasing pectin content. The apparent viscosity values were between 0.0095 and 0.1031 Pa s. SFW addition resulted in a small decrease in viscosity for emulsions formulated with 1 and 2 % PA, but the opposite effect was observed for emulsions formulated with 3 % PA. In addition, shear stress values were higher for emulsions with higher PA content, but were not affected by SFW addition

Physical and mechanical properties of lemon (Citrus lemon) seeds

The objective of this study was to determine some geometric, gravimetric, and mechanical properties of lemon seeds and how these were influenced by moisture content under a range of post-storage processing conditions. The skin, pulp, and seed fractions of lemon fruits were determined. The seed fraction had a value of 1.86% with an average hull/seed ratio of 38.92%. Seed moisture content was varied by drying with hot air from the storage condition (8.28% d.b.) to a minimum moisture condition (1.31% d.b.). The drying kinetics were adequately described using a two-term exponential model, which suggested the presence of two distinct internal seed resistances to moisture transfer related to its composition. Furthermore, with the exception of thickness, all geometric properties evaluated tended to decrease as moisture content decreased, especially at the driest level evaluated. Within these, the most important variations were found in theoretical volume (24.20%) and width (22.28%), for a moisture content change of 84%. Gravimetric and mechanical properties exhibited the same tendency, with the exception of true density, which increased, and bulk density and bulk porosity which did not change significantly. It is noteworthy that rupture energy decreased by approximately 50% as the moisture content was reduced from 8.28 to 4.62%. In conclusion, drying lemon seeds generated smaller and more fragile structures that could benefit subsequent processes such as dehulling or milling, among others, but could also negatively affect seed movement through undesirable breaking. Therefore, knowledge of the properties studied in this work will be useful for the design of manufacturing and storage equipment, as well as handling and process operations