Propionic acid induces apoptosis-like death in Escherichia coli O157.

Propionic acid (PPA), utilized in the manufacture of cellulose acetate propionate, is known to exhibit antimicrobial effects, but its mechanism in Escherichia coli O157 is still unknown. In general, antimicrobial activity is associated with reactive oxygen species (ROS), but ROS generation is not observed under PPA treatment. In addition to ROS, experiments were conducted to observe changes in trehalose and ion balance to discover factors that may affect the cell proliferation. Bacteria use trehalose, a sugar used for stabilization due to stress factors, which contradicts PPA concentration. Discrepancy in homeostasis follows as a result of ion imbalance. PPA causes interruption in bacterial internal stability in a dose-dependent manner. Membrane damage by ion imbalance occurs due to the binding ability of ionized PPA and divalent ions, which induce membrane depolarization, leading to a reduction in cell viability. Considering the lethal impact of membrane depolarization on cell death in bacteria, DNA fragmentation and phosphatidylserine exposure in apoptosis are confirmed. Due to severe damage in DNA, the activation of caspase-like protein is observed. Apoptosis-like death (ALD), a novel programmed cell death in bacteria, occurs eventually. In conclusion, ALD in E. coli O157 is induced via the contribution of homeostasis disruption in a ROS-independent manner.

Proton Transfer Hydrogels: Versatility and Applications.

Proton transfer polymerization between thiol and epoxide groups is shown to be an adaptable and utilitarian method for the synthesis of hydrogels. For instance, the polymerization catalyst can be organic or inorganic, and the polymerization medium can be pure water, buffer solutions, or organic solvents. The gelation mechanism can be triggered at ambient conditions, at a physiological temperature of 37 °C, or through using light as an external stimulus. The ambient and photochemical methods both allow for nanoimprint lithography to produce freestanding patterned thick films. The required thiol- and epoxide-carrying precursors can be chosen from a long list of commercially available small molecular as well as polymeric materials. The water uptake, mechanical, and biodegradation properties of the gels can, therefore, be tuned through the choice of appropriate gelation precursors and polymerization conditions. Finally, the thio-ether groups of the cross-linked networks can be functionalized through a postgelation modification reaction to access sulfonium-based cationic structures. Such structural changes endow antibacterial properties to the networks. In their pristine form, however, the gels are biocompatible and nonadhesive, allowing cancer cells to grow in a cluster formation.

Scapholunate ligament reconstruction using an acellular dermal matrix: a mechanical study.

PURPOSE: Numerous surgical techniques have been described for the treatment of chronic scapholunate ligament instability. We hypothesized that scapholunate ligament reconstruction using an acellular dermal matrix was biomechanically comparable to previously described surgical reconstructions. METHODS: The scaphoid and lunate with the entire scapholunate ligament were harvested from 15 cadaveric specimens. The scapholunate ligament was transected and reconstructed using an acellular dermal matrix (Arthroflex; LifeNet Health, Virginia Beach, VA) and 4 micro suture anchors in 10 specimens. Five specimens were kept with the native scapholunate ligament intact. Five other specimens were reconstructed using a 1.0-mm-thick dermal matrix, and a second cohort of 5 specimens was reconstructed using a 1.5-mm-thick matrix. Tensile testing of all specimens was performed using a servohydraulic material testing system and data acquisition software. The tensile test apparatus applied a distractive load of 10 mm/min (0.17 mm/s) until the specimens reached ultimate failure. Failure force, failure displacement, stiffness, and energy to failure were calculated. RESULTS: All 5 specimens in the intact group failed at the scapholunate ligament midsubstance. The mean ultimate failure force was 172 N, with mean stiffness of 74 N/mm. In the reconstruction group with 1.0-mm dermal matrices, the mode of failure was at the suture-matrix interface in all specimens, whereas the 1.5-mm dermal matrix reconstruction cohort all failed at the bone-suture anchor interface. In the 1.0-mm reconstruction group, the mean ultimate failure force was 77 N, with mean stiffness of 24 N/mm. In the 1.5-mm dermal matrix reconstruction cohort, the mean ultimate failure force was 111 N, with mean stiffness of 30 N/mm. CONCLUSIONS: Scapholunate ligament reconstruction using acellular dermal matrix and suture anchors demonstrated similar biomechanical properties to previously described reconstruction techniques. CLINICAL RELEVANCE: Scapholunate ligament reconstruction using acellular dermal matrix warrants clinical investigation as a potential treatment alternative for chronic scapholunate instability.

Interactions between the plasma membrane and the antimicrobial peptide HP (2-20) and its analogues derived from Helicobacter pylori.

HP (2-20), a 19-residue peptide derived from the N-terminus of Helicobacter pylori ribosomal protein L1, has antimicrobial activity but is not cytotoxic to human erythrocytes. We synthesized several peptide analogues to investigate the effects of substitutions on structure and antimicrobial activity. Replacement of Gln16 and Asp18 with tryptophan [anal-3 (analogue-3)] caused a dramatic increase in lytic activities against bacteria and fungi. By contrast, a decrease in amphiphilicity caused by replacement of Phe5 or Leu11 with serine was accompanied by a reduction in antimicrobial activity. Analysis of the tertiary structures of the peptides in SDS micelles by NMR spectroscopy revealed that they have a well-defined a-helical structure. Among the analogues, anal-3 has the longest a-helix, from Val4 to Trp18. The enhanced hydrophobicity and increased a-helicity results in enhanced antimicrobial activity in anal-3 without an increase in haemolytic activity. Fluorescence experiments proved that the bacterial-cell selectivity of the anal-3 peptide is due to its high binding affinity for negatively charged phospholipids in bacterial cells. Results showing the effect of spin-labels on the NMR spectra indicated that the side chains in the hydrophobic phase of the amphiphilic a-helix are buried on the surface of the micelle and the tryptophan indole ring is anchored in the membrane surface. Because anal-3 shows high selectivity towards bacterial and fungal cells, it may provide an avenue for the development of new antibiotics.