Detrimental Effect of Ozone on Pathogenic Bacteria

(1) Background: Disinfection of medical devices designed for clinical use associated or not with the growing area of tissue engineering is an urgent need. However, traditional disinfection methods are not always suitable for some biomaterials, especially those sensitive to chemical, thermal, or radiation. Therefore, the objective of this study was to evaluate the minimal concentration of ozone gas (O3) necessary to control and kill a set of sensitive or multi-resistant Gram-positive and Gram-negative bacteria. The cell viability, membrane permeability, and the levels of reactive intracellular oxygen (ROS) species were also investigated; (2) Material and Methods: Four standard strains and a clinical MDR strain were exposed to low doses of ozone at different concentrations and times. Bacterial inactivation (cultivability, membrane damage) was investigated using colony counts, resazurin as a metabolic indicator, and propidium iodide (PI). A fluorescent probe (H2DCFDA) was used for the ROS analyses; (3) Results: No reduction in the count colony was detected after O3 exposure compared to the control group. However, the cell viability of E. coli (30%), P. aeruginosa (25%), and A. baumannii (15%) was reduced considerably. The bacterial membrane of all strains was not affected by O3 but presented a significant increase of ROS in E. coli (90 ± 14%), P. aeruginosa (62.5 ± 19%), and A. baumanni (52.6 ± 5%); (4) Conclusion: Low doses of ozone were able to interfere in the cell viability of most strains studied, and although it does not cause damage to the bacterial membrane, increased levels of reactive ROS are responsible for causing a detrimental effect in the lipids, proteins, and DNA metabolism.

Curcumin activation of a bacterial mechanosensitive channel underlies its membrane permeability and adjuvant properties

Curcumin, a natural compound isolated from the rhizome of turmeric, has been shown to have antibacterial properties. It has several physiological effects on bacteria including an apoptosis-like response involving RecA, membrane permeabilization, inhibiting septation, and it can also work synergistically with other antibiotics. The mechanism by which curcumin permeabilizes the bacterial membrane has been unclear. Most bacterial species contain a Mechanosensitive channel of large conductance, MscL, which serves the function of a biological emergency release valve; these large-pore channels open in response to membrane tension from osmotic shifts and, to avoid cell lysis, allow the release of solutes from the cytoplasm. Here we show that the MscL channel underlies the membrane permeabilization by curcumin as well as its synergistic properties with other antibiotics, by allowing access of antibiotics to the cytoplasm; MscL also appears to have an inhibitory role in septation, which is enhanced when activated by curcumin.

Considerations for the Analysis of Bacterial Membrane Vesicles: Methods of Vesicle Production and Quantification Can Influence Biological and Experimental Outcomes

Recent years have seen a surge in interest in the roles of BMVs in host-microbe interactions and interbacterial communication. As a result of such rapid growth in the field, there is a lack of uniformity in BMV enumeration.

An NIR-Triggered Au Nanocage Used for Photo-Thermo Therapy of Chronic Wound in Diabetic Rats Through Bacterial Membrane Destruction and Skin Cell Mitochondrial Protection

Bacterial infection and its severe oxidative stress reaction will cause damage to skin cell mitochondria, resulting in long-lasting wound healing and great pain to patients. Thus, delayed wound healing in diabetic patients with Staphylococcus aureus infection is a principal challenge worldwide. Therefore, novel biomaterials with multifunction of bacterial membrane destruction and skin cell mitochondrial protection are urgently needed to be developed to address this challenge. In this work, novel gold cage (AuNCs) modified with epigallocatechin gallate (EGCG) were prepared to treat delayed diabetic wounds. The results showed that Au-EGCG had a high and stable photothermal conversion efficiency under near-infrared irradiation, and the scavenging rate of Au-EGCG for S. aureus could reach 95%. The production of large amounts of reactive oxygen species (ROS) leads to the disruption of bacterial membranes, inducing bacterial lysis and apoptosis. Meanwhile, Au-EGCG fused into hydrogel (Au-EGCG@H) promoted the migration and proliferation of human umbilical cord endothelial cells, reduced cellular mitochondrial damage and oxidative stress in the presence of infection, and significantly increased the basic fibroblast growth factor expression and vascular endothelial growth factor. In addition, animal studies showed that wound closure was 97.2% after 12 days of treatment, and the healing of chronic diabetic wounds was significantly accelerated. Au-EGCG nanoplatforms were successfully prepared to promote cell migration and angiogenesis in diabetic rats while removing S. aureus, reducing oxidative stress in cells, and restoring impaired mitochondrial function. Au-EGCG provides an effective, biocompatible, and multifunctional therapeutic strategy for chronic diabetic wounds.

Incorporation of Plasmid DNA Into Bacterial Membrane Vesicles by Peptidoglycan Defects in Escherichia coli

Membrane vesicles (MVs) are released by various prokaryotes and play a role in the delivery of various cell-cell interaction factors. Recent studies have determined that these vesicles are capable of functioning as mediators of horizontal gene transfer. Outer membrane vesicles (OMVs) are a type of MV that is released by Gram-negative bacteria and primarily composed of outer membrane and periplasm components; however, it remains largely unknown why DNA is contained within OMVs. Our study aimed to understand the mechanism by which DNA that is localized in the cytoplasm is incorporated into OMVs in Gram-negative bacteria. We compared DNA associated with OMVs using Escherichia coli BW25113 cells harboring the non-conjugative, non-mobilized, and high-copy plasmid pUC19 and its hypervesiculating mutants that included ΔnlpI, ΔrseA, and ΔtolA. Plasmid copy per vesicle was increased in OMVs derived from ΔnlpI, in which peptidoglycan (PG) breakdown and synthesis are altered. When supplemented with 1% glycine to inhibit PG synthesis, both OMV formation and plasmid copy per vesicle were increased in the wild type. The bacterial membrane condition test indicated that membrane permeability was increased in the presence of glycine at the late exponential phase, in which cell lysis did not occur. Additionally, quick-freeze deep-etch and replica electron microscopy observations revealed that outer-inner membrane vesicles (O-IMVs) are formed in the presence of glycine. Thus, two proposed routes for DNA incorporation into OMVs under PG-damaged conditions are suggested. These routes include DNA leakage due to increased membrane permeation and O-IMV formation. Additionally, our findings contribute to a greater understanding of the vesicle-mediated horizontal gene transfer that occurs in nature and the utilization of MVs for DNA cargo.