Leakage Of Intracellular Contents Research Articles

Strong and sustained activation of the anticipatory unfolded protein response induces necrotic cell death.

The endoplasmic reticulum stress sensor, the unfolded protein response (UPR), regulates intracellular protein homeostasis. While transient activation of the reactive UPR by unfolded protein is protective, prolonged and sustained activation of the reactive UPR triggers CHOP-mediated apoptosis. In the recently characterized, evolutionarily conserved anticipatory UPR, mitogenic hormones and other effectors pre-activate the UPR; how strong and sustained activation of the anticipatory UPR induces cell death was unknown. To characterize this cell death pathway, we used BHPI, a small molecule that activates the anticipatory UPR through estrogen receptor α (ERα) and induces death of ERα+ cancer cells. We show that sustained activation of the anticipatory UPR by BHPI kills cells by inducing depletion of intracellular ATP, resulting in classical necrosis phenotypes, including plasma membrane disruption and leakage of intracellular contents. Unlike reactive UPR activation, BHPI-induced hyperactivation of the anticipatory UPR does not induce apoptosis or sustained autophagy. BHPI does not induce CHOP protein or PARP cleavage, and two pan-caspase inhibitors, or Bcl2 overexpression, have no effect on BHPI-induced cell death. Moreover, BHPI does not increase expression of autophagy markers, or work through recently identified programmed-necrosis pathways, such as necroptosis. Opening of endoplasmic reticulum IP3R calcium channels stimulates cell swelling, cPLA2 activation, and arachidonic acid release. Notably, cPLA2 activation requires ATP depletion. Importantly, blocking rapid cell swelling or production of arachidonic acid does not prevent necrotic cell death. Rapid cell death is upstream of PERK activation and protein synthesis inhibition, and results from strong and sustained activation of early steps in the anticipatory UPR. Supporting a central role for ATP depletion, reversing ATP depletion blocks rapid cell death, and the onset of necrotic cell death is correlated with ATP depletion. Necrotic cell death initiated by strong and sustained activation of the anticipatory UPR is a newly discovered role of the UPR.

Photodynamic inactivation of Burkholderia cepacia by curcumin in combination with EDTA

Burkholderia cepacia (B. cepacia) is an aerobic Gram-negative bacillus found in various aquatic environments and can cause food contamination. We investigated the photodynamic antibacterial effects of food additive curcumin combined with EDTA on B. cepacia. We found a ~4-log reduction in B. cepacia viability when photo-irradiated with curcumin at 50 μM by blue LED light (16 mW/cm2) for 30 min with 0.4% (w/v) EDTA. Moreover, the bacterial morphological alterations and the leakage of intracellular contents were observed after photodynamic treatment. There were also obvious genomic DNA cleavage and a general loss of bacterial proteins assigned to large-scale protein degradation after photodynamic inactivation treatment. Collectively, curcumin in combination with EDTA illuminated by blue LED is a potential candidate for photodynamic inactivation of B. cepacia.

The Plant Defensin NaD1 Enters the Cytoplasm of Candida Albicans via Endocytosis.

Antimicrobial peptides are widespread in nature and are produced by many organisms as a first line of defence against pathogens. These peptides have a broad range of biological activities, such as antibacterial or antifungal activities and act with varied mechanisms of action. A large number of the peptides are amphipathic α-helices which act by disrupting plasma membranes and allowing leakage of intracellular contents. However, some peptides have more complex mechanisms of action that require internalisation into the target organisms’ cytoplasm. The method by which these peptides enter the cytoplasm varies, with some requiring the energy dependent processes of endocytosis or polyamine transport and others entering via passive transport. Here we describe the mechanism that the antimicrobial peptide, the plant defensin NaD1, uses to transverse the fungal membrane and gain access to the fungal cytoplasm. By inhibiting ATP synthesis and using an inhibitor of actin polymerisation, we show that NaD1 is internalised into C. albicans yeast cells by the energy-dependent process of endocytosis.

An Optimized Synthetic-Bioinformatic Natural Product Antibiotic Sterilizes Multidrug-Resistant Acinetobacter baumannii-Infected Wounds.

The antibiotic paenimucillin A was originally identified using a culture-independent synthetic-bioinformatic natural product (syn-BNP) discovery approach. Here we report on a bioinformatics-guided survey of paenimucillin A analogs that led to the discovery of paenimucillin C. Paenimucillin C inhibits the growth of multidrug-resistant (MDR) Acinetobacter baumannii clinical isolates, as well as other Gram-negative bacterial pathogens. In a rat cutaneous wound model, it completely sterilized MDR A.baumannii wound infections with no sign of rebound. Mechanistic studies point to a membrane-associated mode of action that results in leakage of intracellular contents. IMPORTANCE Natural product-inspired antibiotics have saved millions of lives and played a critical role in modern medicine. However, the emergence of drug-resistant pathogens is outpacing the rate at which new clinically useful antibiotics are being discovered. The lack of a means to combat infections caused by multidrug-resistant (MDR) Acinetobacter baumannii is of particular concern. The sharp increase in cases of MDR A.baumannii infections in recent years prompted the CDC (https://www.cdc.gov/drugresistance/biggest_threats.html) and WHO (http://www.who.int/medicines/publications/global-priority-list-antibiotic-resistant-bacteria/en/) to list this pathogen as a "serious threat" and "critical pathogen," respectively. Here we report a new antibiotic, paenimucillin C, active against Gram-negative bacterial pathogens, including many clinical isolates of MDR A.baumannii strains. Mechanistic studies point to membrane disruption leading to leakage of intracellular contents as its antibacterial mode of action. Paenimucillin C sterilizes MDR A.baumannii infections in a rat cutaneous wound model with no sign of rebound infection, providing a potential new therapeutic regimen.

Carcinogenesis-relevant biological events in the pathophysiology of the efferocytosis phenomenon.

The effective removal of cells undergoing programmed cell death, which is referred to as efferocytosis, prevents the leakage of intracellular contents into the surrounding tissue, which could lead to tissue damage and inflammation. Efferocytosis involves a coordinated orchestration of multiple steps that lead to a swift, coherent and immunologically silent removal of dying cells. The release of wound healing cytokines, which resolve inflammation and enhance tissue repair, is an important feature of efferocytosis. However, in addition to the healing cytokines released during efferocytosis, the immunosuppressive action of cytokines promotes the tumor microenvironment, enhances the motility of cancer cells and promotes the evasion of antitumor immunity. The aim of the present review was to comprehensively discuss the efferocytosis phenomenon, the important players associated with this process and their role in cancer-related biological events.

Inactivation of four genera of dominant fungal spores in groundwater using UV and UV/PMS: Efficiency and mechanisms

Outbreaks of fungi in groundwater sources of drinking water can produce taste and odor problems, and cause ill health in immunocompromised individuals. The groundwater treatment process is simple; generally, only disinfection is used in China. Efficient disinfection methods to control fungi are required. In the present study, we investigated the inactivation efficiency of 4 dominant genera of fungal spores (a Trichoderma sp., Acremonium sp., Penicillium sp., and Cladosporium sp.) using ultraviolet irradiation (UV) and UV-based advanced oxidation processes, and explored the mechanisms of inactivation by monitoring the leakage of intracellular contents and changes in spore morphology. The inactivation of fungal spores is consistent with first-order Chick–Watson kinetics. The resistance of each of the fungi to UV (Cladosporium sp.>Penicillium sp.>Acremonium sp.>Trichoderma sp.) was greater than that of E. coli, due to their larger sizes and more complex structures. UV/peroxymonosulfate (UV/PMS) treatment had a markedly better inactivation rate constant than UV alone. Furthermore, UV/PMS exhibited similar effects on fungal inactivation in phosphate buffer and in groundwater, whereas UV inactivation efficiency markedly decreased in groundwater. UV/PMS treatment resulted in cell wall and cell membrane damage, the leakage of intracellular contents, and the shriveling of fungal spores, due to the reactive radicals produced by the treatment. Thus, UV/PMS is a promising method to control fungi in drinking water sources.

A truncated Sph12-38 with potent antimicrobial activity showing resistance against bacterial challenge in Oryzias melastigma

Antimicrobial peptides (AMPs) represent an efficient part of innate immunity and are found in a variety of life. Among them Histone 2A (H2A), as a promising class of AMPs, attracts great attention, but the in vivo mechanism of H2A derived AMP is still less known. Based on the acquisition of Sphistin, a synthetic 38-amino acid H2A derived peptide from Scylla paramamosain, as reported in our previous study, was truncated into three short fragments (Sph12-38, Sph20-38 and Sph30-38) and further investigated for its possible functional domains. The antimicrobial activities of these analogs against different Gram-positive bacteria, Gram-negative bacteria and fungi were illustrated. Among the analogs, Sph12-38 showed a stronger activity with a much lower minimum inhibitory concentration (3 μM) against Staphylococcus aureus, Corynebacterium glutamicum, Micrococcus lysodeikticus Fleming, Bacillus subtilis, Pseudomonas fluorescens, Aeromonas hydrophila and A. sobria in comparison with the reported Sphistin. A leakage of intracellular content was described in E. coli treated with Sph12-38. Unlike Sphistin which mainly disrupts the membrane integrity, Sph12-38 could also combine the A. sobria genomic DNA with a minimum concentration of 6 μM and was located intracellularly in cells observed under confocal laser scanning microscope imaging. In comparison with the control group of Oryzias melastigma injected with A. sobria alone, the group treated with a mixture of Sph12-38 and A. sobria showed a higher survival rate 7 days post-injection. Furthermore, in a pretreatment assay at 6 h, a higher survival rate was observed in the group injected with the mixture of Sph12-38 and A. sobria. Taken together, the synthetic peptide of Sph12-38 had a potent antimicrobial activity against bacteria. However, Sph12-38 had no cytotoxicity towards the hemolymph of S. paramamosain. Our study suggested that, as with Sph12-38, the H2A derived peptides were more likely prone to exert their activities in vivo through the truncated fragments while defending against different species of pathogens.

Using scanning and transmission electron microscopy to investigate the antibacterial mechanism of action of the medicinal plant Annona squamosa Linn.

Leaves of Annona squamosa Linn. (Annonaceae), used in traditional medicine for infection treatment and prevention, have been shown to possess antibacterial activity in several recent studies. We examined the effect of the active reticuline-containing fraction of this traditional medicine on bacterial cell ultrastructure to gain insight into its mechanism of action. Bacillus cereus and Campylobacter jejuni were used as representative Gram-positive and Gram-negative pathogens, respectively. Time-kill assays were performed with each bacterial species and 1xMIC (minimum inhibitory concentration), 2xMIC, 1xMBC (minimum bactericidal concentration) and 2xMBC levels of A. squamosa extract to identify treatment times and concentrations at which inhibitory and bactericidal effects occur. Treated bacteria were then examined by scanning and transmission electron microscopy. The results showed that in B. cereus populations treated with inhibitory concentrations of extract, peptidoglycan distribution was altered, cell shape was distorted, and cells were up to 6.9 times their normal length. Inhibitory concentrations caused no changes in C. jejuni cell shape or length, but separation of the cell wall layers was observed together with leakage of intracellular contents. In B. cereus and C. jejuni populations treated with bactericidal concentrations of extract, the cell envelope was compromised and the cytoplasm depleted. These results suggest A. squamosa extract inhibits bacterial growth by disrupting peptidoglycan formation, with cell death probably occurring due to loss of the wall’s mechanical strength and osmotic lysis.

Effects of low-density lipoproteins as additive on quality parameters and oxidative stress following cryopreservation of mithun (Bos frontalis) spermatozoa.

Artificial breeding of mithun poses several challenges including lack of standard protocol for cryopreservation of spermatozoa. This is further complicated by harmful effects of hen's egg yolk (EY) as additive in extender. Purified low-density lipoproteins (LDL) extracted from EY have been shown as beneficial over EY extender for long-term semen storage in several species. This investigation explored use of LDL versus EY on semen quality and oxidative stress following freezing-thawing of spermatozoa. A total of 25 of 50 ejaculates based on biophysical parameters were selected for the experiment. After diluting with the Tris-citrate-glycerol (TCG) extender, each sample was split into three equal aliquots: Group I, control, EY; Group II and Group III contained 8% and 10% purified LDL, respectively. Frozen-thawed samples were evaluated for motility parameters (progressive, and in the bovine cervical mucus penetration test [BCMPT]), viability, sperm and nuclear abnormality, acrosome integrity, and enzymatic (leakage of intracellular contents) and biochemical (oxidative stress) profiles and in vitro fertility (IVF) assay. Study revealed a significant (p<.05) improvement in viability, sperm and nuclear abnormality, acrosome integrity, motility (progressive and in cervical mucus), cholesterol content, and reduction in the leakage of intracellular enzymes in Group II. Moreover, intactness of acrosome and biochemical membranes was protected significantly (p<.05) in addition to significant (p<.05) improvement in binding per cent and binding index in IVF assay in extender containing 8% LDL. These results demonstrate that although cryopreservation of mithun's spermatozoa in EY was comparable with other species, addition of 8% LDL holds a clear advantage over EY or 10% LDL.

Biological Effect and Inactivation Mechanism of Bacillus subtilis Exposed to Pulsed Magnetic Field: Morphology, Membrane Permeability and Intracellular Contents

Biological effect and inactivation mechanism of Bacillus subtilis exposed to pulsed magnetic field (PMF) were investigated. Cell morphology, membrane permeability, release of intracellular proteins and damage of deoxyribonucleic acid (DNA) were monitored. The inactivation effect of PMF treatment on B. subtilis was enhanced with the increase in intensity and pulse number. Scanning electron microscopy (SEM) analysis showed that the PMF treated bacterial cells had rough surfaces and damaged cellular membranes. Flow cytometry measurements showed that the cell membrane permeability increased after the PMF treatment. Leakage of intracellular contents, measured as OD, significantly increased with the increase in PMF intensity and pulsed number. A maximum leakage of cytoplasmic contents was detected at intensity of 3.30 T and 30 pulses. Enterobacterial repetitive intergenic consensus - polymerase chain reaction (ERIC-PCR) fingerprint signaled that the DNA was fragmented after the PMF treatment at the intensity of 3.0 T with 30 pulses and 3.3 T with 10, 20 and 30 pulses. These findings may give clues to the mechanism of bacterial cell death due to the PMF treatment.

Evaluation of antibacterial effect of magnesium oxide nanoparticles with nisin and heat in milk

Objective(s): The objective of this study was to investigate the antibacterial activities of magnesium oxide nanoparticles (MgO NP) alone or in combination with other antimicrobials (nisin and heat) against Escherichia coli and Staphylococcus aureus in milk.Materials and Methods: First, the combined effect of nisin and MgO nanoparticles was investigated in milk. Then the combined effect of nisin, heat and MgO nanoparticles was assessed in milk. Also the scanning electron microscopy was used to characterize the morphological changes of S. aureus before and after antimicrobial treatments.Results: The results showed that MgO NP have strong bactericidal activity against the pathogens. A synergistic effect of MgO in combination with nisin and heat was observed as well. Scanning electron microscopy was revealed that MgO NP treatments in combination with nisin distort and damage the cell membrane, resulting in a leakage of intracellular contents and eventually the death of bacterial cells. Conclusion: These results suggested that MgO NP alone or in combination with nisin could potentially be used as an effective antibacterial agent to enhance food safety.

Investigation into the antibacterial behavior of suspensions of magnesium oxide nanoparticles in combination with nisin and heat against Escherichia coli and Staphylococcus aureus in milk

The antibacterial activities of magnesium oxide nanoparticles (MgO NP) alone or in combination with nisin against Escherichia coli and Staphylococcus aureus were investigated. Synergistic antibacterial effects existed and at lower levels of nisin when compared to when nisin was used alone. Also the antibacterial activities of MgO NP in combination with other antimicrobials (nisin and heat) against E. coli and S. aureus were investigated in milk. A synergistic effect of MgO NP in combination with nisin and heat was observed as well. Scanning electron microscopy was used to characterize the morphological changes of E. coli after antimicrobial treatments. It was revealed that MgO NP treatments in combination with nisin distort and damage the cell membrane, resulting in a leakage of intracellular contents and eventually the death of bacterial cells. This is the first report describing the antibacterial activity of MgO NPs and nisin in milk. It leads the way to development of treatment combinations which could result in a decrease in pasteurisation temperatures and the level of MgO NP required for pasteurising milk and maintaining pathogen control.

Microbial glycolipoprotein-capped silver nanoparticles as emerging antibacterial agents against cholera.

BackgroundWith the increased number of cholera outbreaks and emergence of multidrug resistance in Vibrio cholerae strains it has become necessary for the scientific community to devise and develop novel therapeutic approaches against cholera. Recent studies have indicated plausibility of therapeutic application of metal nano-materials. Among these, silver nanoparticles (AgNPs) have emerged as a potential antimicrobial agent to combat infectious diseases. At present nanoparticles are mostly produced using physical or chemical techniques which are toxic and hazardous. Thus exploitation of microbial systems could be a green eco-friendly approach for the synthesis of nanoparticles having similar or even better antimicrobial activity and biocompatibility. Hence, it would be worth to explore the possibility of utilization of microbial silver nanoparticles and their conjugates as potential novel therapeutic agent against infectious diseases like cholera.ResultsThe present study attempted utilization of Ochrobactrum rhizosphaerae for the production of AgNPs and focused on investigating their role as antimicrobial agents against cholera. Later the exopolymer, purified from the culture supernatant, was used for the synthesis of spherical shaped AgNPs of around 10 nm size. Further the exopolymer was characterized as glycolipoprotein (GLP). Antibacterial activity of the novel GLP–AgNPs conjugate was evaluated by minimum inhibitory concentration, XTT reduction assay, scanning electron microscopy (SEM) and growth curve analysis. SEM studies revealed that AgNPs treatment resulted in intracellular contents leakage and cell lysis.ConclusionThe potential of microbially synthesized nanoparticles, as novel therapeutic agents, is still relatively less explored. In fact, the present study first time demonstrated that a glycolipoprotein secreted by the O. rhizosphaerae strain can be exploited for production of AgNPs which can further be employed to treat infectious diseases. Although this type of polymer has been obtained earlier from marine fungi and bacteria, none of these reports have studied the role of this polymer in AgNPs synthesis and its application in cholera therapy. Interestingly, the microbial GLP-capped AgNPs exhibited antibacterial activity against V. cholerae comparable to ciprofloxacin. Thus the present study may open up new avenues for development of novel therapeutic agents for treatment of infectious diseases.Graphical abstractDevelopment of novel therapeutic agents for treatment of cholera

Ultrastructural changes in methicillin-resistant Staphylococcus aureus induced by positively charged silver nanoparticles.

Silver nanoparticles offer a possible means of fighting antibacterial resistance. Most of their antibacterial properties are attributed to their silver ions. In the present work, we study the actions of positively charged silver nanoparticles against both methicillin-sensitive Staphylococcus aureus and methicillin-resistant Staphylococcus aureus. We use aberration-corrected transmission electron microscopy to examine the bactericidal effects of silver nanoparticles and the ultrastructural changes in bacteria that are induced by silver nanoparticles. The study revealed that our 1 nm average size silver nanoparticles induced thinning and permeabilization of the cell wall, destabilization of the peptidoglycan layer, and subsequent leakage of intracellular content, causing bacterial cell lysis. We hypothesize that positively charged silver nanoparticles bind to the negatively charged polyanionic backbones of teichoic acids and the related cell wall glycopolymers of bacteria as a first target, consequently stressing the structure and permeability of the cell wall. This hypothesis provides a major mechanism to explain the antibacterial effects of silver nanoparticles on Staphylococcus aureus. Future research should focus on defining the related molecular mechanisms and their importance to the antimicrobial activity of silver nanoparticles.

Drugs and Rhabdomyolysis: From Liver to Kidney.

Rhabdomyolysis is a syndrome due to a damage of skeletal muscle and the leakage of intracellular contents into the extracellular fluid and the circulation. Several causes may induce rhabdomyolysis and the major one is the crush syndrome. Most cases of non-traumatic rhabdomyolysis are related to drugs. Many molecules are subject to hepatic metabolism and the concomitant use of drugs, as statins, with other medications acting as substrates of the same isoenzymes can interact and increase the risk of myopathy. Subclinical rise of creatine kinase may be the expression of rhabdomyolysis that can present as a medical emergency such as acute kidney injury (AKI), compartment syndrome, cardiac dysrhythmias and disseminated intravascular coagulopathy. The main pathophysiological mechanisms of myoglobinuric-related AKI are renal vasoconstriction, formation of intraluminal casts and direct cytotoxicity promoted by heme-protein. The aim of this review is to analyze the pathophysiology of myolysis, the causes of rhabdomyolysis and especially the link between the liver and the kidney, which can represent the connecting element for the development of the syndrome.

Pentobra: A Potent Antibiotic with Multiple Layers of Selective Antimicrobial Mechanisms against Propionibacterium Acnes

Although antibiotics are a common treatment for acne, the difficulties inherent to effective antimicrobial penetration in sebum and selective antimicrobial action in skin are compounded by increasing resistance of Propionibacterium acnes clinical isolates. To address these problems, we engineered Pentobra, a peptide-aminoglycoside molecule which has multiple mechanisms of antibacterial action, and investigated whether it can be a potential candidate for the treatment of acne. Pentobra combines the potent ribosomal activity of aminoglycosides with the bacteria-selective membrane-permeabilizing abilities of antimicrobial peptides (AMPs). Pentobra demonstrated potent and selective killing of P. acnes, but not against human skin cells in vitro. In direct comparison, Pentobra demonstrated bactericidal activity and drastically outperformed free tobramycin (by 5–7 logs) against multiple P. acnes clinical strains. Moreover, EM studies showed that Pentobra had robust membrane activity, as treatment with Pentobra killed P. acnes cells and caused leakage of intracellular contents. Pentobra may also have potential anti-inflammatory effects as demonstrated by suppression of some P. acnes-induced chemokines. Importantly, the killing activity was maintained in sebaceous environments as Pentobra was bactericidal against clinical isolates in comedones extracts isolated from human donors. Our work demonstrates that equipping aminoglycosides with selective membrane activity is a viable approach for developing antibiotics against P. acnes that are effective in cutaneous environments.

Efferocytosis creates a tumor microenvironment supportive of tumor survival and metastasis.

Programmed cell death, or apoptosis, occurs in nearly all tissues of all multi-cellular organisms. In order to avoid leakage of intracellular contents, which could generate tissue damaging inflammation, apoptotic cells are cleared from tissues by phagocytes, which then dispatch the engulfed dying cell through the lysosomal pathway. Phagocytic clearance of apoptotic cells is referred to as efferocytosis. One key feature of efferocytosis is the production and release of wound healing cytokines by the phagocyte, which acts to resolve inflammation, and promote tissue repair. Phagocytic engulfment of apoptotic cells coupled with cytokine modulation aimed at immune suppression ensures that physiological programmed cell death does not induce inflammation and tissue damage. However, cytokines involved in wound healing and immune suppression are notorious for their role in the tumor microenvironment, increasing tumor cell motility and promoting evasion of anti-tumor immunity. Therefore, current and future studies aimed at targeting important players of efferocytosis should reveal new and efficacious therapeutic approaches for limiting cancer progression and relapse.

Synthesis, characterization, antimicrobial activity and mechanism of a novel hydroxyapatite whisker/nano zinc oxide biomaterial

Postoperative infections remain a risk factor that leads to failures in oral and maxillofacial artificial bone transplantation. This study aimed to synthesize and evaluate a novel hydroxyapatite whisker (HAPw) / nano zinc oxide (n-ZnO) antimicrobial bone restorative biomaterial. A scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD) were employed to characterize and analyze the material. Antibacterial capabilities against Staphylococcus aureus, Escherichia coli, Candida albicans and Streptococcus mutans were determined by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), and kinetic growth inhibition assays were performed under darkness and simulated solar irradiation. The mode of antibiotic action was observed by transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). The MIC and MBC were 0.078–1.250 mg ml−1 and 0.156–2.500 mg ml−1, respectively. The inhibitory function on the growth of the microorganisms was achieved even under darkness, with gram-positive bacteria found to be more sensitive than gram-negative, and enhanced antimicrobial activity was exhibited under simulated solar excitation compared to darkness. TEM and CLSM images revealed a certain level of bacterial cell membrane destruction after treatment with 1 mg ml−1 of the material for 12 h, causing the leakage of intracellular contents and bacteria death. These results suggest favorable antibiotic properties and a probable mechanism of the biomaterial for the first time, and further studies are needed to determine its potential application as a postoperative anti-inflammation method in bone transplantation.

Tolerance of Salmonella enterica serovar Typhimurium to nisin combined with EDTA is accompanied by changes in cellular composition

Nisin has been widely used in many countries, as a food additive for dairy products and canned vegetables and fruits. Although Gram-negative bacteria have natural resistance to nisin due to the presence of the outer membrane, the use of chelating agents, such as EDTA, allows for their sensitization. However, Salmonella can alter the composition and the structure of their lipopolysaccharide layer (LPS) in response to changes in environmental conditions, and thus mitigate their sensitivity to bacteriocins, such as nisin. In this study, we demonstrated and characterized tolerance to nisin combined with EDTA in Salmonella Typhimurium cultured under specific conditions of temperature and pH by means of assays of growth, viability, leakage of intracellular content and Fourier transform infrared spectroscopy (FT-IR). The modifications related to the tolerance phenotype to nisin combined with EDTA possibly involve changes in the phospholipid acyl chains, in the sugar content of LPS and in the peptidoglycan present in the cell wall. These findings demonstrate the importance of better understanding the behavior of the cells treated with nisin and EDTA, especially due to widespread use of this bacteriocin in food preservation.

Evaluation of morphological changes of Staphylococcus aureus and Escherichia coli induced with the antimicrobial peptide AN5-1.

The mechanisms of action of AN5-1 against Gram-negative and Gram-positive bacteria were investigated by evaluations of the intracellular content leakage and by microscopic observations of the treated cells. Escherichia coli and Staphylococcus aureus were used for this investigation. Measurements of DNA, RNA, proteins, and β-galactosidase were taken, and the results showed a significant increase in the cultivation media after treatment with AN5-1 compared with the untreated cells. The morphological changes of treated cells were shown using transmission electron microscopy (TEM) and atomic force microscopy (AFM). The observations showed that AN5-1 acts against E. coli and against S. aureus in similar ways, by targeting the cell wall, causing disruptions; at a high concentration (80 AU/ml), these disruptions led to cell lysis. The 3D AFM imaging system showed that at a low concentration of 20 AU/ml, the effect of AN5-1 is restricted to pore formation only. Moreover, a separation between the cell wall and the cytoplasm was observed when Gram-negative bacteria were treated with a low concentration (20 AU/ml) of AN5-1.