Bactericidal Mode of Action of Plantaricin C

Plantaricin C is a bacteriocin produced by Lactobacillus plantarum LL441 that kills sensitive cells by acting on the cytoplasmic membrane. In contrast to its lack of impact on immune cells, plantaricin C dissipates the proton motive force and inhibits amino acid transport in sensitive cells. In proteoliposomes, plantaricin C dissipates the transmembrane electrical potential, and in liposomes, it elicits efflux of entrapped carboxy-fluorescein. It is concluded that plantaricin C is a pore-forming bacteriocin that functions in a voltage-independent manner and does not require a specific protein receptor in the target membrane.     

Bactericidal Performance of Visible-Light Responsive Titania Photocatalyst with Silver Nanostructures

Background

Titania dioxide (TiO₂) photocatalyst is primarily induced by ultraviolet light irradiation. Visible-light responsive anion-doped TiO₂ photocatalysts contain higher quantum efficiency under sunlight and can be used safely in indoor settings without exposing to biohazardous ultraviolet light. The antibacterial efficiency, however, remains to be further improved.

Methodology/Principal Findings

Using thermal reduction method, here we synthesized silver-nanostructures coated TiO₂ thin films that contain a high visible-light responsive antibacterial property. Among our tested titania substrates including TiO₂, carbon-doped TiO₂ [TiO₂ (C)] and nitrogen-doped TiO₂ [TiO₂ (N)], TiO₂ (N) showed the best performance after silver coating. The synergistic antibacterial effect results approximately 5 log reductions of surviving bacteria of Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus and Acinetobacter baumannii. Scanning electron microscope analysis indicated that crystalline silver formed unique wire-like nanostructures on TiO₂ (N) substrates, while formed relatively straight and thicker rod-shaped precipitates on the other two titania materials.

Conclusion/Significance

Our results suggested that proper forms of silver on various titania materials could further influence the bactericidal property.     

Effects of Silver Nanoparticles and Silver Nitrate on Antioxidant Responses in Echium amoenum

Russian Journal of Plant Physiology - Nanoparticles have entered agriculture and biology fields because of their special effects and unique features. One of the most important properties of silver...     

Properties and Mode of Action of a Bactericidal Compound (= Methylglyoxal) Produced by a Mutant of Escherichia coli

A lethal product (BPG) produced by a glycerol kinase mutant of Escherichia coli was purified, and its mode of action on E. coli was studied. At concentrations where BPG strongly inhibits in vivo deoxyribonucleic acid, ribonucleic acid, and protein synthesis, it produces small effects on other functions: slight inhibition of respiration and small changes in intracellular pools of substrates, nucleic acids degradation, and adenosine triphosphate levels. BPG also inhibits in vitro protein synthesis and produces inactivation of bacteriophage T4. The bactericidal product has been identified in another laboratory as methylglyoxal (MG). By comparing BPG and MG, we confirmed this observation and concluded that the activity found in our BPG preparation is due to its MG content. We also observed that MG is able to react with guanosine triphosphate. According to these results, it is interpreted that MG could act directly on macromolecular synthesis by reacting with the guanine residues of nucleic acids and its precursors.     

Morphological and Proteomic Responses of Eruca sativa Exposed to Silver Nanoparticles or Silver Nitrate

Silver nanoparticles (AgNPs) are widely used in commercial products, and there are growing concerns about their impact on the environment. Information about the molecular interaction of AgNPs with plants is lacking. To increase our understanding of the mechanisms involved in plant responses to AgNPs and to differentiate between particle specific and ionic silver effects we determined the morphological and proteomic changes induced in Eruca sativa (commonly called rocket) in response to AgNPs or AgNO₃. Seedlings were treated for 5 days with different concentrations of AgNPs or AgNO₃. A similar increase in root elongation was observed when seedlings were exposed to 10 mg Ag L¹ of either PVP-AgNPs or AgNO₃. At this concentration we performed electron microscopy investigations and 2-dimensional electrophoresis (2DE) proteomic profiling. The low level of overlap of differentially expressed proteins indicates that AgNPs and AgNO₃ cause different plant responses. Both Ag treatments cause changes in proteins involved in the redox regulation and in the sulfur metabolism. These responses could play an important role to maintain cellular homeostasis. Only the AgNP exposure cause the alteration of some proteins related to the endoplasmic reticulum and vacuole indicating these two organelles as targets of the AgNPs action. These data add further evidences that the effects of AgNPs are not simply due to the release of Ag ions.     

Insights into the Mechanism of Action of Bactericidal Lipophosphonoxins

The advantages offered by established antibiotics in the treatment of infectious diseases are endangered due to the increase in the number of antibiotic-resistant bacterial strains. This leads to a need for new antibacterial compounds. Recently, we discovered a series of compounds termed lipophosphonoxins (LPPOs) that exhibit selective cytotoxicity towards Gram-positive bacteria that include pathogens and resistant strains. For further development of these compounds, it was necessary to identify the mechanism of their action and characterize their interaction with eukaryotic cells/organisms in more detail. Here, we show that at their bactericidal concentrations LPPOs localize to the plasmatic membrane in bacteria but not in eukaryotes. In an in vitro system we demonstrate that LPPOs create pores in the membrane. This provides an explanation of their action in vivo where they cause serious damage of the cellular membrane, efflux of the cytosol, and cell disintegration. Further, we show that (i) LPPOs are not genotoxic as determined by the Ames test, (ii) do not cross a monolayer of Caco-2 cells, suggesting they are unable of transepithelial transport, (iii) are well tolerated by living mice when administered orally but not peritoneally, and (iv) are stable at low pH, indicating they could survive the acidic environment in the stomach. Finally, using one of the most potent LPPOs, we attempted and failed to select resistant strains against this compound while we were able to readily select resistant strains against a known antibiotic, rifampicin. In summary, LPPOs represent a new class of compounds with a potential for development as antibacterial agents for topical applications and perhaps also for treatment of gastrointestinal infections.     

Mechanism of the Bactericidal Action Produced by Electrohydraulic Shock

Electrohydraulic shock was shown to produce oxidation reactions which inactivated certain compounds important in cellular metabolism. Enzymes that were inactivated included lactic dehydrogenase, trypsin, and proteinases of Bacillus subtilis. Free sulfhydryl groups and reduced nicotinamide adenine dinucleotide were oxidized. Adenosine triphosphate was destroyed, but deoxyribonucleic acid was not affected. Intracellular material of Escherichia coli lost its ability to absorb at 260 mmu after electrohydraulic shock. The bactericidal mechanism involved appeared to be due to nonselective oxidation reactions produced by high-voltage discharges in water. These oxidation reactions were probably mediated by free radicals produced in the water.     

Bactericidal Action of Fresh Rabbit Blood Against Brucella abortus

A photometric method was used to measure the bactericidal kinetics for Brucella abortus of freshly drawn rabbit blood during the time before clotting. This antibrucellar activity varied between rabbits in different immunologic states. Nonimmunized rabbits had moderate bactericidal activity after a lag of about 2 min. The blood of some immunized rabbits gave an immediate and strong kill, but in certain other immunized rabbits, especially when hyperimmunized, the bactericidal activity was inhibited. It appeared that serum bactericidins and complement are sometimes as active in unclotted blood as they are in serum. However, this bactericidal activity can be either increased or neutralized by immunization. The prozone bactericidal inhibition phenomenon (Neisser-Wechsberg) found in immune serum may, in fact, reflect inhibition taking place in vivo. Inhibition of the bactericidal activity in blood can contribute to the persistence of chronic infections and individual variations in resistance.     

New Facts about CdCl2 Action on the Photosynthetic Apparatus of Spinach Chloroplasts and Its Comparison with HgCl2 Action

Using EPR spectroscopy it was found that CdCl₂ and HgCl₂ interact (1) with the intermediates , i.e. with the tyrosine radicals on the donor side of photosystem (PS) 2 situated in the 161^st position in D₁ and D₂ proteins; (2) with the primary donor of PS1 (P700) whereby the oxidation of chlorophyll (Chl) a dimer in the reaction centre of PS1 occurs yet in the dark; (3) with the manganese cluster which is situated in the oxygen evolving complex. Due to these interactions of investigated metal chlorides with the photosynthetic apparatus, the interruption of the photosynthetic electron transport through photosynthetic centres occurs. Monitoring of time dependence of EPR signal I of chloroplasts treated with CdCl₂ or HgCl₂ after switching off the light suggests that all mechanisms, i.e. direct, cyclic, and non-cyclic reductions of P700⁺ are damaged. The formation of complexes between mercury or cadmium ions and amino acid residues constituting photosynthetic peptides was suggested as possible mechanism of their inhibitory action. The higher HgCl₂ efficiency in comparison with that of CdCl₂ was explained by higher ability of mercury ions to form complexes with amino acids, what was demonstrated by their apparent binding constants: K = 10 200 M^–1 for Hg²⁺ ions, and K = 3 700 M^–1 for Cd²⁺ ions.