Direct injection of functional single-domain antibodies from E. coli into human cells

Intracellular proteins have a great potential as targets for therapeutic antibodies (Abs) but the plasma membrane prevents access to these antigens. Ab fragments and IgGs are selected and engineered in E. coli and this microorganism may be also an ideal vector for their intracellular delivery. In this work we demonstrate that single-domain Ab (sdAbs) can be engineered to be injected into human cells by E. coli bacteria carrying molecular syringes assembled by a type III protein secretion system (T3SS). The injected sdAbs accumulate in the cytoplasm of HeLa cells at levels ca. 10⁵–10⁶ molecules per cell and their functionality is shown by the isolation of sdAb-antigen complexes. Injection of sdAbs does not require bacterial invasion or the transfer of genetic material. These results are proof-of-principle for the capacity of E. coli bacteria to directly deliver intracellular sdAbs (intrabodies) into human cells for analytical and therapeutic purposes.     

The Pepsin Hydrolysate of Bovine Lactoferrin Causes a Collapse of the Membrane Potential in Escherichia coli O157:H7

In the present study, the ability of bovine lactoferrin hydrolysate (LfH) to disrupt the cytoplasmic membrane of Escherichia coli O157:H7 was investigated. Lactoferrin and LfH antimicrobial activities were compared against E. coli O157:H7 and E. coli O157:H7 spheroplasts. The effect of LfH on the cytoplasmic membrane of E. coli O157:H7 cells was determined by evaluating potassium efflux (K⁺), dissipation of ATP and membrane potential (ΔΨ). LfH produced a rapid efflux of potassium ions, a decrease in intracellular levels of ATP coupled with a substantial increase in extracellular ATP levels and a complete dissipation of the ΔΨ. The results suggest that LfH causes a collapse of the membrane integrity by pore formation in the inner membrane, leading to the death of the cell. Moreover, the mechanism of action of LfH on E. coli O157:H7 appears to involve an interference with the inner membrane integrity based on experiments using E. coli O157:H7 spheroplasts.     

Thermolysis of recombinant Escherichia coli for recovering a thermostable enzyme

The development of recombinant DNA has made it feasible to produce a wide range of valuable protein products in the bacterium Escherichia coli. Extraction of intracellular protein from E. coli is traditionally achieved by mechanical, chemical or enzymatic disruption technology. In this study, thermolysis, which differs from the traditional ones, is presented for disruption of E. coli cells to release recombinant thermostable enzyme. Heat treatment of E. coli at 80 °C is highly effective to destroy the integrity of the bacterial cell wall and release the recombinant thermostable enzyme. At the same time of disruption, the recombinant thermostable enzyme was partially purified. Moreover, thermolysis was carried out in fermentation broth in situ, which may make it a more applicable approach for industrial-scale processes.     

Effects of Toluene and Phenethyl Alcohol on the Ultrastructure of Escherichia coli

Treatment of Escherichia coli cells with 0.25% toluene caused partial dissolution of the plasma membrane concomitant with displacement of nuclear material towards the cell periphery. By contrast, treatment with 0.25% phenethyl alcohol generated intracellular membranes.     

Erythrocyte Sensitization by Blood Group-Specific Bacterial Antigens

Human and chicken erythrocytes are readily coated in vitro by blood group active protein-lipopolysaccharides and lipopolysaccharides from E. coli O₈₆ and E. coli O₁₂₈. Serum albumin, α₂- and β-lipoproteins inhibit this sensitization. Blood group B specific agglutination of erythrocytes with B or B-like antigens was obtained with antibodies purified by adsorption on and elution from B erythrocytes. Anti-blood group B and E. coli O₈₆-specific antibodies could be eluted from E. coli O₈₆-coated O erythrocytes. Eel anti-H(O) serum agglutinated O erythrocytes and only those A₁B red cells which were coated with blood group H(O) active E. coli products. Blood group active substances specifically inhibited agglutination of lipopolysaccharide-coated erythrocytes by anti-B and anti-H(O) agglutinins. Demonstrable amounts of lipopolysaccharide could only be removed from coated erythrocytes by washing them at elevated temperatures (58°C) in physiological solutions. Red cell sensitization with B active E. coli O₈₆ substances was achieved in vivo in a minority of severely diseased infants and in germ-free and ordinary chicks which were in tourniquet shock after treatment with cathartics. Therefore, a possible mode by which erythrocytes of patients with severe intestinal disorders acquire antigens is the fixation of bacterial substances to their surfaces, if there are not enough of the normally interfering plasma factors present.     

Arabidopsis dynamin‐related protein 1E in sphingolipid‐enriched plasma membrane domains is associated with the development of freezing tolerance

The freezing tolerance of Arabidopsis thaliana is enhanced by cold acclimation, resulting in changes in the compositions and function of the plasma membrane. Here, we show that a dynamin‐related protein 1E (DRP1E), which is thought to function in the vesicle trafficking pathway in cells, is related to an increase in freezing tolerance during cold acclimation. DRP1E accumulated in sphingolipid and sterol‐enriched plasma membrane domains after cold acclimation. Analysis of drp1e mutants clearly showed that DRP1E is required for full development of freezing tolerance after cold acclimation. DRP1E fused with green fluorescent protein was visible as small foci that overlapped with fluorescent dye‐labelled plasma membrane, providing evidence that DRP1E localizes non‐uniformly in specific areas of the plasma membrane. These results suggest that DRP1E accumulates in sphingolipid and sterol‐enriched plasma membrane domains and plays a role in freezing tolerance development during cold acclimation.     

Effect of oleoyl-chitosan nanoparticles as a novel antibacterial dispersion system on viability,membrane permeability and cell morphology of Escherichia coli and Staphylococcus aureus

A novel chitosan antibacterial dispersion system was prepared by oleoyl-chitosan (O-chitosan) nanoparticles (OCNP) and the bactericidal activity against Escherichia coli and Staphylococcus aureus was evaluated by the enumeration of viable organisms at different incubation times. We further investigated the antimicrobial mode of OCNP using a combination of approaches, including cell integrity measurements, outer membrane (OM) and inner membrane (IM) permeabilization assays, SDS–PAGE and transmission electron microscopy (TEM). Results showed that when treated with OCNP, release of intracellular components quickly increased for both E. coli and S. aureus. OCNP also rapidly increased the 1-N-phenylnaphthylamine (NPN) uptake and the release of cytoplasmic β-galactosidase via increasing the permeability of OM and IM. Besides, SDS–PAGE indicated the content of cellular soluble proteins decreased significantly in OCNP-treated bacteria. TEM observations demonstrated adsorption behaviors of OCNP on bacteria and extensive cell surface alterations of OCNP-treated bacteria. OCNP has potential value in the determination of antibacterial mechanism of chitosan.     

Evaluation of Ultrasound-Induced Damage to Escherichia coli and Staphylococcus aureus by Flow Cytometry and Transmission Electron Microscopy

As a nonthermal sterilization technique, ultrasound has attracted great interest in the field of food preservation. In this study, flow cytometry and transmission electron microscopy were employed to investigate ultrasound-induced damage to Escherichia coli and Staphylococcus aureus. For flow cytometry studies, single staining with propidium iodide (PI) or carboxyfluorescein diacetate (cFDA) revealed that ultrasound treatment caused cell death by compromising membrane integrity, inactivating intracellular esterases, and inhibiting metabolic performance. The results showed that ultrasound damage was independent of initial bacterial concentrations, while the mechanism of cellular damage differed according to the bacterial species. For the Gram-negative bacterium E. coli, ultrasound worked first on the outer membrane rather than the cytoplasmic membrane. Based on the double-staining results, we inferred that ultrasound treatment might be an all-or-nothing process: cells ruptured and disintegrated by ultrasound cannot be revived, which can be considered an advantage of ultrasound over other nonthermal techniques. Transmission electron microscopy studies revealed that the mechanism of ultrasound-induced damage was multitarget inactivation, involving the cell wall, cytoplasmic membrane, and inner structure. Understanding of the irreversible antibacterial action of ultrasound has great significance for its further utilization in the food industry.     

Impedimetric analysis on the mass transfer properties of intact and competent E. coli cells

Competent Escherichia coli cells are commonly used in bacterial transformation owing to its high permeability for bioorganic macromolecules like plasmid DNA. However, the mass transfer property of competent E. coli cell has not fully investigated. In the present study, mass transfer coefficients of competent and intact E. coli cells in deionized water were evaluated by impedimetric analysis of the release of cytoplasmic compounds. Because competent cells have a higher permeability after chemical treatment, the lumped mass transfer coefficient of a competent cell was approximately 6.5 times larger than that of an intact cell at room temperature. Release of cytoplasmic components was accelerated at an elevated temperature of 42?°C, which is the heat shock temperature used during bacterial transformation. At this elevated temperature, assessed lumped mass transfer coefficients of intact and competent E. coli cells were 9.28?×?10^?4?min^?1 and 97.10?×?10^?4?min^?1, respectively. Significant increase in the mass transfer coefficient of the competent cell is caused by cytolysis of cells. The double layer capacitances were also assessed from the electrochemical spectra confirming the enhanced ion release from E. coli cells and rupture of the competent cell under prolonged exposure at the elevated temperature. Impedimetric detection of the ion release with analyses using an equivalent circuit model provides a method to evaluate mass transfer properties of biomolecules.     

Rates of chilling to 0°C: implications for the survival of microorganisms and relationship with membrane fluidity modifications

The effects of slow chilling (2°C min⁻¹) and rapid chilling (2,000°C min⁻¹) were investigated on the survival and membrane fluidity of Escherichia coli, of Bacillus subtilis, and of Saccharomyces cerevisiae. Cell death was found to be dependent on the physiological state of cell cultures and on the rate of temperature downshift. Slow temperature decrease allowed cell stabilization, whereas the rapid chilling induced an immediate loss of viability of up to more than 90 and 70% for the exponentially growing cells of E. coli and B. subtilis, respectively. To relate the results of viability with changes in membrane physical state, membrane anisotropy variation was monitored during thermal stress using the fluorescence probe 1,6-diphenyl-1,3,5-hexatriene. No variation in the membrane fluidity of all the three microorganisms was found after the slow chilling. It is interesting to note that fluorescence measurements showed an irreversible rigidification of the membrane of exponentially growing cells of E. coli and B. subtilis after the instantaneous cold shock, which was not observed with S. cerevisiae. This irreversible effect of the rapid cold shock on the membrane correlated well with high rates of cell inactivation. Thus, membrane alteration seems to be the principal cause of the cold shock injury.     

Induction of lysozymelike activity in the hemolymph and hemocytes of an insect, Spodoptera eridania

Lysozymelike activity is present in the hemocytes and cell-free hemolymph of Spodoptera eridania. Its level remains essentially constant during larval development and can be induced by injection of various foreign materials. Serum bacteriolytic activity rises 24 hr after injection of saline, BSA, bacteria, bacterial endotoxin (LPS), latex particles, or sham injection. However, the magnitude and subsequent duration of the response depends on the nature of the injected material. The response is transient following sham injection or injection of soluble substances, such as saline and BSA, as compared to treatment with latex or bacteria. Both soluble and insoluble fractions of bacterial LPS preparations stimulated the lysozyme response. The response to a single injection of E. coli LPS was dose dependent and persisted for at least 5 days; however, additional injections had no effect on serum lysozyme level. The basal intracellular lysozyme level was significantly increased by E. coli LPS injection. Lysozyme release by hemocytes was proportional to intracellular concentration and did not increase after phagocytic stimulation of hemocytes.     

Disinfection of ocular cells and tissues by atmospheric-pressure cold plasma

Background

Low temperature plasmas have been proposed in medicine as agents for tissue disinfection and have received increasing attention due to the frequency of bacterial resistance to antibiotics. This study explored whether atmospheric-pressure cold plasma (APCP) generated by a new portable device that ionizes a flow of helium gas can inactivate ocular pathogens without causing significant tissue damage.

Methodology/Principal Findings

We tested the APCP effects on cultured Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Candida albicans, Aspergillus fumigatus and Herpes simplex virus-1, ocular cells (conjunctival fibroblasts and keratocytes) and ex-vivo corneas. Exposure to APCP for 0.5 to 5 minutes significantly reduced microbial viability (colony-forming units) but not human cell viability (MTT assay, FACS and Tunel analysis) or the number of HSV-1 plaque-forming units. Increased levels of intracellular reactive oxygen species (ROS) in exposed microorganisms and cells were found using a FACS-activated 2′,7′-dichlorofluorescein diacetate probe. Immunoassays demonstrated no induction of thymine dimers in cell cultures and corneal tissues. A transient increased expression of 8-OHdG, genes and proteins related to oxidative stress (OGG1, GPX, NFE2L2), was determined in ocular cells and corneas by HPLC, qRT-PCR and Western blot analysis.

Conclusions

A short application of APCP appears to be an efficient and rapid ocular disinfectant for bacteria and fungi without significant damage on ocular cells and tissues, although the treatment of conjunctival fibroblasts and keratocytes caused a time-restricted generation of intracellular ROS and oxidative stress-related responses.     

The interaction betweenE. coli spheroplasts and plant protoplasts: A proposed procedure to deliver foreign genes into plant cells

Summary E. coli spheroplasts can be used to deliver DNA vectors into plant protoplasts. The use of fluorescent dyes showed that 25–100% of the protoplast population was associated with 1–9 spheroplasts following incubation with several fusogens. Electron microscopy demonstrated spheroplasts attached to protoplasts via a plasma membrane protrusion after high pH/Ca²⁺ treatment, but PEG-high pH/Ca²⁺ promoted endocytosis of spheroplasts into a plasma membrane bounded vesicle. Ultrastructural profiles showed that fusion between spheroplasts and protoplasts did not occur. Immunofluorescence studies detectedE. coli antigens associated with tobacco protoplasts, and after fusogen treatment the antigens were dispersed within the peripheral cytoplasm. The elimination of residual contaminatingE. coli cells from protoplasts was achieved by lysozyme and antibiotic treatment, thus allowing DNA vector assessment in axenic culture.     

Changes in bacterial cells induced by high pressure at subzero temperature

The aim of this study was to examine the effect of pressure treatment at 193 MPa and −20 °C on membrane damage, changes in activity of membrane-bound ATPases and degradation of nucleic acids. The experiments were carried out with three Escherichia coli strains, in the exponential and stationary phases of growth, and differing in sensitivity to pressure. All E. coli strains subjected to pressure in the exponential phase of growth were inactivated by 6 log cycles, independently of the strain, which was accompanied by a total loss of ability to plasmolyse, an increase in irreversible membrane permeability to PI, and a reduction of cellular ATP by more than 80%. After pressure treatment of stationary phase cells, the relationship between the inactivation level and the ability to plasmolyse was not as evident as in the case of exponential phase cells. Pressure treatment of two strains of E. coli K-12 and Ec160/59 in the stationary phase that decreased viability by no more than one log cycle led only to reversible permeabilization of bacterial membranes, while irreversible permeabilization was observed in the pressure sensitive E. coli IBA72 strain phase that was inactivated by 4.6 log cycles. The reduction of ATP and changes in ATPase activity after pressure treatment of tested E. coli strains in the stationary phase of growth depended on the stage of inactivation of the particular strain. Electrophoretic analysis showed degradation of RNA isolated after pressure treatment from cells of all E. coli strains tested in the exponential phase of growth. The changes of RNA induced by pressure were not visible in the case of cells in the stationary phase. The degradation of DNA isolated from pressure treated E. coli strains from the exponential as well as from the stationary phase of growth was not observed.     

Membrane Damage and Microbial Inactivation by Chlorine in the Absence and Presence of a Chlorine-Demanding Substrate

The relationship between cell inactivation and membrane damage was studied in two gram-positive organisms, Listeria monocytogenes and Bacillus subtilis, and two gram-negative organisms, Yersinia enterocolitica and Escherichia coli, exposed to chlorine in the absence and presence of 150 ppm of organic matter (Trypticase soy broth). L. monocytogenes and B. subtilis were more resistant to chlorine in distilled water. The addition of small amounts of organic matter to the chlorination medium drastically increased the resistance of both types of microorganisms, but this effect was more marked in Y. enterocolitica and E. coli. In addition, the survival curves for these microorganisms in the presence of organic matter had a prolonged shoulder. Sublethal injury was not detected under most experimental conditions, and only gram-positive cells treated in distilled water showed a relevant degree of injury. The exposure of bacterial cells to chlorine in distilled water caused extensive permeabilization of the cytoplasmic membrane, but the concentrations required were much higher than those needed to inactivate cells. Therefore, there was no relationship between the occurrence of membrane permeabilization and cell death. The addition of organic matter to the treatment medium stabilized the cytoplasmic membrane against permeabilization in both the gram-positive and gram-negative bacteria investigated. Exposure of E. coli cells to the outer membrane-permeabilizing agent EDTA increased their sensitivity to chlorine and caused the shoulders in the survival curves to disappear. Based on these observations, we propose that bacterial envelopes could play a role in cell inactivation by modulating the access of chlorine to the key targets within the cell.     

Global metabolomics characterization of bacteria: pre-analytical treatments and profiling

Pre-analytical treatments of bacteria are crucial steps in bacterial metabolomics studies. In order to achieve reliable samples that can best represent the global metabolic profile in vivo both qualitatively and quantitatively, many sample treatment procedures have been developed. The use of different methods makes it difficult to compare the results among different groups. In this work, E. coli samples were tested by using NMR spectroscopy. Both liquid N₂ and cold methanol quenching procedures reduce the cell membrane integrity and cause metabolites leakage. However, liquid N₂ quenching affected the cell viability and the NMR metabolites’ profile less than cold methanol procedure. Samples obtained by metabolite extraction were significantly superior over cell suspensions and cell lysates, with a higher number of detectable metabolites. Methanol/chloroform extraction proved most efficient at extraction of intracellular metabolites from both qualitative and quantitative points of view. Finally, standard operating procedures of bacterial sample treatments for NMR metabolomics study are presented.     

Different modes in antibiotic action of tritrpticin analogs, cathelicidin-derived Trp-rich and Pro/Arg-rich peptides

The cathelicidin-derived antimicrobial tritrpticin could be classified as either Trp-rich or Pro/Arg-rich peptide. We recently found that the sequence modification of tritrpticin focused on Trp and Pro residues led to considerable change in structure and antimicrobial potency and selectivity, but their mechanisms of microbial killing action were still unclear. Here, to better understand the bactericidal mechanisms of tritrpticin and its two analogs, TPA and TWF, we studied their effect on the viability of Gram-positive S. aureus and Gram-negative E. coli in relation to their membrane depolarization. Although TWF more effectively inhibited growth of S. aureus and E. coli than TPA, only a 30 min exposure to TPA was sufficient to kill both bacteria and TWF required a lag period of about 3-6 h for bactericidal activity. Their different bactericidal kinetics was associated with membrane permeabilization, i.e., TWF showed negligible ability to depolarize the cytoplasmic membrane potential of target cell membrane, whereas we observed significant membrane depolarization for TPA. In addition, while TPA caused rapid and large dye leakage from negatively charged model vesicles, TWF showed very little membrane-disrupting activity. Interestingly, we have looked for a synergism among the three peptides against E. coli, supporting that they are working with different modes of action. Collectively, our results suggest that TPA disrupts the ion gradients across the membrane, causing depolarization and a loss of microbial viability. By contrast, TWF more likely translocates across the cytoplasmic membrane without depolarization and then acts against one or more intracellular targets. Tritrpticin exhibits intermediate properties and appears to act via membrane depolarization coupled to secondary intracellular targeting.     

Induction of Oxidative Stress by High Hydrostatic Pressure in Escherichia coli

Using leaderless alkaline phosphatase as a probe, it was demonstrated that pressure treatment induces endogenous intracellular oxidative stress in Escherichia coli MG1655. In stationary-phase cells, this oxidative stress increased with the applied pressure at least up to 400 MPa, which is well beyond the pressure at which the cells started to become inactivated (200 MPa). In exponential-phase cells, in contrast, oxidative stress increased with pressure treatment up to 150 MPa and then decreased again, together with the cell counts. Anaerobic incubation after pressure treatment significantly supported the recovery of MG1655, while mutants with increased intrinsic sensitivity toward oxidative stress (katE, katF, oxyR, sodAB, and soxS) were found to be more pressure sensitive than wild-type MG1655. Furthermore, mild pressure treatment strongly sensitized E. coli toward t-butylhydroperoxide and the superoxide generator plumbagin. Finally, previously described pressure-resistant mutants of E. coli MG1655 displayed enhanced resistance toward plumbagin. In one of these mutants, the induction of endogenous oxidative stress upon high hydrostatic pressure treatment was also investigated and found to be much lower than in MG1655. These results suggest that, at least under some conditions, the inactivation of E. coli by high hydrostatic pressure treatment is the consequence of a suicide mechanism involving the induction of an endogenous oxidative burst.     

Bactericidal effect of Naja nigricollis toxin γ is related to its membrane-damaging activity

The aim of the present study is to investigate the causal relationship between membrane-damaging activity and bactericidal activity of Naja nigricollis toxin γ. Toxin γ showed a similar inhibitory activity on the growth of Staphylococcus aureus (Gram-positive bacteria) and Escherichia coli (Gram-negative bacteria). Antibacterial activity of toxin γ correlated positively with increase in membrane permeability of bacterial cells. Morphological examination showed that toxin γ disrupted the integrity of bacterial membrane. Toxin γ showed similar binding capability with lipopolysaccharide (LPS) and lipoteichoic acid (LTA), and destabilization of LPS layer and inhibition of LTA biosynthesis on cell wall increased bactericidal effect of toxin γ on E. coli and S. aureus, respectively. Although the potency of toxin γ on permeabilzing model membrane of E. coli and S. aureus was similar, the mode of interaction between toxin γ and model membrane of E. coli and S. aureus differed. Membrane-damaging activity of toxin γ was inhibited by either LPS or LTA. Nevertheless, LPS and LTA altered differently membrane-bound conformation of toxin γ. Taken together, our data suggest that bactericidal activity of toxin γ depends on its ability to induce membrane permeability, and that LPS and LTA structurally suppresses bactericidal effect of toxin γ.     

Evaluation of cell damage caused by cold sampling and quenching for metabolome analysis

Cell damage during sampling and quenching for metabolome analysis have been investigated at whole sample level using an OD-based method and ATP loss investigation, and at single cell level by means of flow cytometry. Escherichia coli was cultivated in shake flasks and sampled into several cold quenching solutions during exponential growth phase varying quenching solution composition and sampling temperature. For single cell analysis, the samples were incubated with selective propidium iodide dye and analysed via flow cytometry to differentiate between intact and damaged cells. It was found that every combination of quenching solution, temperature, or cooling rate tested influenced the E. coli cell membrane integrity indicating rupture which will not only let the dye in, but also intracellular ATP out of the cells, which is not desired in in vivo metabolome analysis.