Atomic force microscopic study on morphological alterations induced by photodynamic action of Toluidine Blue O in Staphylococcus aureus and Escherichia coli

Date (Phoenix dactylifera L.) seed oil is an agro-industrial waste with biopreservative effects and antimicrobial activity

Antimicrobial resistant (AMR) infections are a leading health threat globally. Previous literature has underscored the farm-to-fork continuum as a potential focal point for the emergence and spread of AMR. In the present study, date (Phoenix dactylifera L.) seed oil was investigated for its chemical composition and antimicrobial activity against common foodborne pathogens including Escherichia coli O157:H7, Salmonella enteritidis, Salmonella typhimurium, Listeria monocytogenes, and Staphylococcus aureus in vitro, and in ultra-high-temperature (UHT) milk as a food model at storage temperatures of 37 °C (24 h) and 10 °C (7 days). GC-MS analysis of the seed oil revealed 20 compounds, with octadecane (52.2-55.4%) as the major constituent, and the fatty acid analysis revealed 17 fatty acids, with oleic acid (42.3-43.1%) as the main constituent, followed by lauric acid (19.8-20.3%). The antimicrobial activity of date seed oil was determined using the microdilution method. A significant inhibition against gram-negative bacteria was noted in microbiological media and UHT milk, with a log reduction ranging from 4.3 to 6.7 (at 37 °C/24 h) and 5.7 to 7.2 (at 10 °C/7 days), respectively, at oil concentrations ranging between 10 and 15 µl/ml. The oil showed a similar significant inhibitory effect against St. aureus in the microbiological media (2.0-6.0 log reduction), whereas the inhibitory effect against L. monocytogenes was not statistically significant, with a maximum log reduction of 0.64 achieved at a concentration of 10 µl/ml. AFM imaging of the bacteria showed that oil treatment led to morphological changes in the bacteria including the formation of distorted shapes, surface blebs, indentations, stiffness, and swelling. Present findings suggest that date seed oil can be a promising by-product with potential antimicrobial activity and a food preservative.

Synthesis and photodynamic antimicrobial chemotherapy against multi-drug resistant Proteus mirabilis of ornithine-porphyrin conjugates in vitro and in vivo

For the treatment of bacterial infections, photodynamic antimicrobial chemotherapy (PACT) has the advantage of circumventing multi-drug resistance. In this work, new cationic photosensitizers against multi-drug resistant Proteus mirabilis (MRPM) were designed and synthesized by the conjugation of amino phenyl porphyrin with basic amino acid L-ornithine. Their photoinactivation efficacies against MRPM in vitro were reported and include the influence of laser energy, uptake, MIC and MBC, dose-dependent photoinactivation effects, membrane integrity, and fluorescence imaging. The PACT in vivo was evaluated using a wound mouse model infected by MRPM. Photosensitizer 4d displayed high photo inactivation efficacy against MRPM at 7.81 μM under illumination, and it could accelerate wound healing via bactericidal effect. These ornithine-porphyrin conjugates are potential photosensitizers for PACT in the treatment of MRPM infection.

Understanding the role of surface interactions in the antibacterial activity of layered double hydroxide nanoparticles by atomic force microscopy

Understanding the mechanisms of the interactions between zinc-based layered double hydroxides (LDHs) and bacterial surfaces is of great importance to improve the efficiency of these antibiotic-free antibacterial agents. In fact, the role of surface interactions in the antibacterial activity of zinc-based LDH nanoparticles compared to that of dissolution and generation of reactive oxygen species (ROS) is still not well documented. In this study, we show that ZnAl LDH nanoparticles exhibit a strong antibacterial effect against Staphylococcus aureus by inducing serious cell wall damages as revealed by the antibacterial activity tests and atomic force microscopy (AFM) imaging, respectively. The comparison of the antibacterial properties of ZnAl LDH nanoparticles and micron-sized ZnAl LDHs also demonstrated that the antibacterial activity of Zn-based LDHs goes beyond the simple dissolution into Zn²⁺ antibacterial ions. Furthermore, we developed an original approach to functionalize AFM tips with LDH films in order to probe their interactions with living S. aureus cells by means of AFM-based force spectroscopy (FS). The force spectroscopy analysis revealed that antibacterial ZnAl LDH nanoparticles show specific recognition of S. aureus cells with high adhesion frequency and remarkable force magnitudes. This finding provides a first insight into the antibacterial mechanism of Zn-based LDHs through direct surface interactions by which they are able to recognize and adhere to bacterial surfaces, thus damaging them and leading to subsequent growth inhibition.

Interaction with teichoic acids contributes to highly effective antibacterial activity of graphene oxide on Gram-positive bacteria

Graphene oxide (GO) has high-efficient antibacterial activity to diverse pathogenic bacteria. However, the detailed antibacterial mechanism of GO is not fully clear. Herein the antibacterial properties of GO against model Gram-positive (Gram+) (Staphylococcus aureus and Staphylococcus epidermidis) and Gram-negative (Gram-) bacteria (Pseudomonas aeruginosa and Escherichia coli) were compared by plate count method. Results showed that 4 mg/L of GO induced the mortality of Gram+ and Gram- bacteria by > 99% and < 25%, respectively. GO had greater adsorption affinity to teichoic acids, the unique components existing in the cell wall of Gram+ bacteria, mainly via π-π interaction. The adsorption efficiency of teichoic acids was 27 times higher than that of peptidoglycan when they were simultaneously exposed to 100 mg/L GO. The superior adsorption of teichoic acids onto GO increased one order of magnitude of atlA expression, the autolysin related gene. As a result, these accelerated bacterial death by hydrolyzing peptidoglycan in cell walls. Exogenous addition of 50 mg/L teichoic acids could impair 4-5 fold of antibacterial activity of GO against S. aureus. These new findings illuminate the antibacterial mechanism of GO against Gram+ bacteria, which paves the way for the further application of graphene-based materials in water disinfection and pathogen control.

Induced photo-cytotoxicity on prostate cancer cells with the photodynamic action of toluidine Blue ortho

BACKGROUND

Photodynamic therapy (PDT) has become an advantageous therapeutic approach for the treatment of select cancers and microbial infections. PDT generates toxic reactive oxygen species as an end product of the interaction between the photosensitizer and light with an appropriate wavelength. Toluidine blue ortho is a photosensitizer that is commonly used in the photodynamic treatment of bacterial infection and a promising photosensitizer for cancer treatment. This study aims to evaluate the potential photo-cytotoxicity of toluidine blue ortho-mediated photodynamic therapy on PC-3 prostate cancer cells.

METHODS

In this study toluidine blue ortho-mediated photodynamic therapy was assessed on PC-3 cancer cells with various photosensitizer concentrations and light energy densities of the 655-nm diode laser. MTT analysis was used for the determination of the cytotoxicity on the cells and viability/cytotoxicity assay was used for live/dead cell staining after the applications. The mechanism of this application was further analyzed with the determination of intracellular reactive oxygen species and nitric oxide release.

RESULTS

The light applications and the photosensitizer alone did not inhibit the cell viability of PC-3 cells. 20 J/cm² laser energy density together with 100 μM photosensitizer concentration resulted in maximum cancer cell death with a rate of approximately 89 %. The level of intracellular reactive oxygen species increased with the increasing parameters of the applications that resulted in more cell death.

CONCLUSION

This study showed the successful anticancer activity of toluidine blue ortho upon irradiation with 655 nm of laser light against PC-3 cancer cells and it was mediated with the production of reactive oxygen species.

Photodynamic effect of TPP encapsulated in polystyrene nanoparticles toward multi-resistant pathogenic bacterial strains: AFM evaluation

Photodynamic inactivation (PDI) is a promising approach for the efficient killing of pathogenic microbes. In this study, the photodynamic effect of sulfonated polystyrene nanoparticles with encapsulated hydrophobic 5,10,15,20-tetraphenylporphyrin (TPP-NP) photosensitizers on Gram-positive (including multi-resistant) and Gram-negative bacterial strains was investigated. The cell viability was determined by the colony forming unit method. The results showed no dark cytotoxicity but high phototoxicity within the tested conditions. Gram-positive bacteria were more sensitive to TPP-NPs than Gram-negative bacteria. Atomic force microscopy was used to detect changes in the morphological properties of bacteria before and after the PDI treatment.

Polyacrylic Acid with Methylene Blue Dye as a Sensitizing Agent for Photodynamic Therapy to Reduce Streptococcus mutans in Dentinal Caries

Objective: To evaluate 11.5% polyacrylic acid (PA) containing 0.3% methylene blue (MB) dye as a photosensitizer for photodynamic therapy (PDT) of carious dentin. Methods: One hundred twenty molars were selected and the dentin was exposed for cariogenic challenge, where the molars were placed in brain heart infusion medium containing a standard strain of Streptococcus mutans (ATCC). Samples were randomly divided into eight groups (n = 15): S: saline, PA, MB: MB 0.3%, PA+MB: PA containing 0.3% MB + LLL: irradiation with low-level laser, PDT (MB): MB 0.3% + laser, PDT (PA): PA + laser, and PDT (PA+MB): PA containing 0.3% MB + laser. Carious dentin was collected before and after exposure to S. mutans. All samples of carious dentin were homogenized, diluted, and seeded in mitis salivarius bacitracin medium, and the cultures were incubated at 37°C for 15 days in anaerobic jars. The Wilcoxon test was used for analysis. Results: The percent microbial reduction achieved with each treatment was as follows: PDT (MB), 53.62%; PDT (PA+MB), 50.47%; PDT (PA), 46.73%; PA, 38.51%; MB, 19.75%; PA+MB, 17.18%; LLL, 12.83%; S, 5.99%. The greatest reductions in S. mutans growth occurred with PDT (MB), PDT (PA+MB), and PDT (PA) when compared to the S group (p = 0.0002, 0.0023, and 0.0232, respectively). Conclusions: PA containing 0.3% MB can be used as a photosensitizer for PDT to reduce S. mutans burden in carious dentin.

Photodynamic antimicrobial chemotherapy in mice with Pseudomonas aeruginosa-infected wounds

This study examined the antibacterial effect of protoporphyrin IX–ethylenediamine derivative (PPIX-ED)–mediated photodynamic antimicrobial chemotherapy (PPIX-ED-PACT) against Pseudomonas aeruginosa in vitro and in vivo. PPIX-ED potently inhibited the growth of Pseudomonas aeruginosa by inducing reactive oxygen species production via photoactivation. Atomic force microscopy revealed that PPIX-ED-PACT induced the leakage of bacterial content by degrading the bacterial membrane and wall. As revealed using acridine orange/ethidium bromide staining, PPIX-ED-PACT altered the permeability of the bacterial membrane. In addition, the antibacterial effect of PPIX-ED-PACT was demonstrated in an in vivo model of P. aeruginosa-infected wounds. PPIX-ED (100 μM) decreased the number of P. aeruginosa colony-forming units by 4.2 log₁₀. Moreover, histological analysis illustrated that the wound healing rate was 98% on day 14 after treatment, which was 10% higher than that in the control group. According to the present findings, PPIX-ED-PACT can effectively inhibit the growth of P. aeruginosa in vitro and in vivo.

Plantaricin NC8 αβ exerts potent antimicrobial activity against Staphylococcus spp. and enhances the effects of antibiotics

The use of conventional antibiotics has substantial clinical efficacy, however these vital antimicrobial agents are becoming less effective due to the dramatic increase in antibiotic-resistant bacteria. Novel approaches to combat bacterial infections are urgently needed and bacteriocins represent a promising alternative. In this study, the activities of the two-peptide bacteriocin PLNC8 αβ were investigated against different Staphylococcus spp. The peptide sequences of PLNC8 α and β were modified, either through truncation or replacement of all L-amino acids with D-amino acids. Both L- and D-PLNC8 αβ caused rapid disruption of lipid membrane integrity and were effective against both susceptible and antibiotic resistant strains. The D-enantiomer was stable against proteolytic degradation by trypsin compared to the L-enantiomer. Of the truncated peptides, β1–22, β7–34 and β1–20 retained an inhibitory activity. The peptides diffused rapidly (2 min) through the bacterial cell wall and permeabilized the cell membrane, causing swelling with a disorganized peptidoglycan layer. Interestingly, sub-MIC concentrations of PLNC8 αβ substantially enhanced the effects of different antibiotics in an additive or synergistic manner. This study shows that PLNC8 αβ is active against Staphylococcus spp. and may be developed as adjuvant in combination therapy to potentiate the effects of antibiotics and reduce their overall use.

Optimization of hydrogel containing toluidine blue O for photodynamic therapy in treating acne

Antibiotics and photodynamic therapy (PDT) are widely employed in curing acne. However, antibiotics as an effective treatment would lead to bacterial resistance and severe side effects. In this study, we aimed to develop a novel TBO hydrogel, which could prolong the retention time of photosensitizer (TBO) at the lesion site and improve therapeutic effect. In vitro antibacterial experiments (against Staphylococcus aureus and Escherichia coli), the response surface methodology was used to optimize the formulation of TBO hydrogel. The results indicated that the optimal formulation was 0.5% (v/v) carbomer, 0.01 mg/mL TBO, 0.5% (v/v) ethanol concentration, 0.5% (v/v) Tween 80, the mass ratio of NaOH to carbomer of 0.4 (w/w). The TBO hydrogel formulation showed the strong antibacterial activity for Propionibacterium acnes. The stability, pH, and antibacterial activity of TBO hydrogel did not significantly change under 4 °C, 25 °C, and 40 °C during 6-week storage. Furthermore, TBO combined with carbomer hydrogel showed the 51.28% (4 h) and 69.80% (24 h) release. In summary, the hydrogel TBO might be a vital therapeutic strategy to promote the PDT applied in the topical therapy of acne. Graphical abstract A TBO hydrogel for photodynamic therapy in the treatment of acne.

Antimicrobial photodynamic activity of toluidine blue encapsulated in mesoporous silica nanoparticles against Pseudomonas aeruginosa and Staphylococcus aureus

In the present study, the antimicrobial and antibiofilm efficacy of toluidine blue (TB) encapsulated in mesoporous silica nanoparticles (MSN) was investigated against Pseudomonas aeruginosa and Staphylococcus aureus treated with antimicrobial photodynamic therapy (aPDT) using a red diode laser 670 nm wavelength, 97.65 J cm^-2 radiant exposure, 5 min). Physico-chemical techniques (UV-visible (UV-vis) absorption, photoluminescence emission, excitation, and FTIR) and high-resolution transmission electron microscopy (HR-TEM) were employed to characterize the conjugate of TB encapsulated in MSN (TB MSN). TB MSN showed maximum antimicrobial activities corresponding to 5.03 and 5.56 log CFU ml^-1 reductions against P. aeruginosa and S. aureus, respectively, whereas samples treated with TB alone showed 2.36 and 2.66 log CFU ml^-1 reductions. Anti-biofilm studies confirmed that TB MSN effectively inhibits biofilm formation and production of extracellular polymeric substances by P. aeruginosa and S. aureus.

Discovery of Distinctin-Like-Peptide-PH (DLP-PH) From the Skin Secretion of Phyllomedusa hypochondrialis, a Prototype of a Novel Family of Antimicrobial Peptide

Amphibian skin secretions are an important treasure house of bioactive antimicrobial peptides (AMPs). Despite having been the focus of decades of research in this context, investigations of phyllomedusine frogs continue to identify new AMPs from their skin secretions. In this study, the prototype of a novel family of AMP distinctin-like-peptide-PH (DLP-PH) was identified from the skin secretion of the otherwise well-studied Tiger-Legged Tree Frog Phyllomedusa hypochondrialis through cloning of its precursor-encoding cDNA from a skin secretion-derived cDNA library by a 3′-rapid amplification of cDNA ends (RACE) strategy. Subsequently, the mature peptide was isolated and characterized using reverse-phase HPLC and MS/MS fragmentation sequencing. DLP-PH adopted an α-helical conformation in membrane mimetic solution and demonstrated unique structural features with two distinct domains that differed markedly in their physiochemical properties. Chemically synthesized replicates of DLP-PH showed antimicrobial activity against planktonic bacterial and yeast cells, but more potent against Escherichia coli at 32 μg/mL. However, DLP-PH showed much weaker inhibitory activity against the growth of sessile cells in biofilms. In addition, DLP-PH exhibited anti-proliferative activity against human cancer cell lines, H157, and PC3, but with no major toxicity against normal human cell, HMEC-1. These combined properties make DLP-PH deserving further study as an antimicrobial agent and further investigations of its structure-activity relationship could provide valuable new insights into drug lead candidates for antimicrobial and/or anti-cancer purposes.

Photosensitizer in lipid nanoparticle: a nano-scaled approach to antibacterial function

Photosensitization-based antimicrobial therapy (PAT) is an alternative therapy aimed at achieving bacterial inactivation. Researchers use various photosensitizers to achieve bacterial inactivation. However, the most widely used approach involves the use of photosensitizers dispersed in aqueous solution, which could limit the effectiveness of photodynamic inactivation. Therefore, the approaches to encapsulate the photosensitizer in appropriate vehicles can enhance the delivery of the photosensitizer. Herein, Toluidine Blue O (TBO) was the photosensitizer, and lipid nanoparticles were used for its encapsulation. The lipid nanoparticle-based delivery system has been tailor-made for decreasing the average size and viscosity and increasing the formulation stability as well as the wettability of skin. Usage of an appropriate vehicle will also increase the cellular uptake of the photosensitizer into the bacterial cells, leading to the damage on cell membrane and genomic DNA. Evidence of effectiveness of the developed PAT on planktonic bacteria and biofilms was examined by fluorescence microscopy and scanning electron microscopy. Lipid nanoparticles protected the photosensitizer from aggregation and made the application easy on the skin as indicated in data of size distribution and contact angle. The use of lipid nanoparticles for encapsulating TBO could enhance photosensitization-based antimicrobial therapy as compared to the aqueous media for delivering photosensitizers.

Targeted Modification of a Novel Amphibian Antimicrobial Peptide from Phyllomedusa tarsius to Enhance Its Activity against MRSA and Microbial Biofilm

Antimicrobial peptides (AMPs) in the skin secretions of amphibians are fundamental components of a unique defense system that has evolved to protect these hosts from microbial invasion. Medusins constitute a recently-discovered AMP family from phyllomedusine leaf frog skin and exhibit highly-conserved structural characteristics. Here, we report a novel medusin, medusin-PT, from the skin secretion of the Tarsier Leaf Frog, Phyllomedusa tarsius. The mature peptide was initially identified from its cloned biosynthetic precursor-encoding cDNA as obtained by the rapid amplification of cDNA ends (RACE) method. Reverse-phase HPLC and tandem mass spectrometry confirmed both the presence of medusin-PT in the skin secretion and its primary structure. In a range of bioassays, medusin-PT exhibited antimicrobial activity against only the Gram-positive bacterium Staphylococcus aureus at 64 μg/ml. However, after directed changes to enhance the cationicity and amphipathicity of the peptide structure, three analog showed more potent antimicrobial activity against several additional bacteria including the antibiotic-resistant bacterium MRSA. In addition, these analog exhibited activity against microbial biofilm (minimum biofilm inhibitory and eradication concentrations of 32 μg/ml and over 64 μg/ml, respectively). These data provide evidence that medusins might be promising candidates as novel antibiotic leads and that the targeted modification of a natural AMP can both improve its efficacy so as to provide new insights into antibiotic design and development.

Photodynamic inactivation of fibroblasts and inhibition of Staphylococcus epidermidis adhesion and biofilm formation by toluidine blue O

Treating skin and soft tissue infections of severe limb traumas can be challenging. Crucial concerns focus on inhibiting biofilm formation by antibiotic‑resistant bacteria, and preventing scar formation by fibroblastic hyperproliferation. The local use of toluidine blue O (TBO)‑mediated photodynamic therapy (PDT) may be a promising strategy for treating such lesions. The present study used Staphylococcus epidermidis (strain ATCC 35984) to assess the effects of TBO‑PDT on bacterial adherence and biofilm formation, using confocal laser scanning microscopy (CLSM), tissue culture plating (TCP) and scanning electron microscopy (SEM). Primary human fibroblast cells were used to evaluate the cytotoxicity of TBO‑PDT using the 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide (MTT) assay and CLSM. Six different treatment groups were investigated: Medium only [tryptone soy broth (TSB) or Dulbecco's modified Eagle's medium (DMEM)]; red light control (light dose, 30 J/cm2); TBO group (50 mM TBO); TBO‑PDT1 (TBO irradiated with 10 J/cm2); TBO‑PDT2 (TBO irradiated with 20 J/cm2); and TBO‑PDT3 (TBO irradiated with 30 J/cm2). The results of the S. epidermidis adhesion assay indicated that the TSB, light and TBO groups exhibited significant bacterial adherence, compared with the TBO‑PDT groups. Analysis of biofilm formation revealed significant light dose‑dependent differences between the TBO‑PDT groups and the TSB, light, and TBO groups. Furthermore, SEM indicated fewer colony masses in the TBO‑PDT groups compared with the control groups. The MTT assay for fibroblastic cell toxicity demonstrated ~1.1, 4.6, 14.5, 29.7 and 43.4% reduction in optical density for the light, TBO, TBO‑PDT1, TBO‑PDT2 and TBO‑PDT3 groups, respectively, compared with the DMEM control group. There was no difference in toxicity between the light and control groups, however, there were significant differences among the TBO‑PDT groups. Finally, alterations in fibroblast morphology and cell spreading were revealed by CLSM, following TBO‑PDT treatment. TBO‑PDT inhibited bacterial adhesion and biofilm formation, and exhibited significant cytotoxic effects on human fibroblasts. These results indicate that the local use of TBO‑PDT in limb lesions may be a useful treatment method for inhibiting bacterial biofilm formation and fibroblastic hyperproliferation, which may prevent infectious hypertrophic scar formation.

Factors Determining Staphylococcus aureus Susceptibility to Photoantimicrobial Chemotherapy: RsbU Activity, Staphyloxanthin Level, and Membrane Fluidity

Photoantimicrobial chemotherapy (PACT) constitutes a particular type of stress condition, in which bacterial cells induce a pleiotropic and as yet unexplored effect. In light of this, the key master regulators are of putative significance to the overall phototoxic outcome. In Staphylococcus aureus, the alternative sigma factor σ^B controls the expression of genes involved in the response to environmental stress. We show that aberration of any sigB operon genes in S. aureus USA300 isogenic mutants causes a pronounced sensitization (>5 log₁₀ reduction in CFU drop) to PACT with selected photosensitizers, namely protoporphyrin diarginate, zinc phthalocyanine and rose bengal. This effect is partly due to aberration-coupled staphyloxanthin synthesis inhibition. We identified frequent mutations in RsbU, a σ^B activator, in PACT-vulnerable clinical isolates of S. aureus, resulting in σ^B activity impairment. Locations of significant changes in protein structure (IS256 insertion, early STOP codon occurrence, substitutions A230T and A276D) were shown in a theoretical model of S. aureus RsbU. As a phenotypic hallmark of PACT-vulnerable S. aureus strains, we observed an increased fluidity of bacterial cell membrane, which is a result of staphyloxanthin content and other yet unidentified factors. Our research indicates σ^B as a promising target of adjunctive antimicrobial therapy and suggests that enhanced cell membrane fluidity may be an adjuvant strategy in PACT.

Overall biochemical changes in bacteria photosensitized with cationic porphyrins monitored by infrared spectroscopy

BACKGROUND

Photodynamic inactivation of micro-organisms is a promising nonantibiotic multitarget approach to treat localized and superficial infections through oxidative stress. Herein, the changes occurring on major cellular components of Escherichia coli and Staphylococcus warneri, induced by photosensitization with cationic porphyrins (Tri-Py(+)-Me-PF and Tetra-Py(+)-Me) and white light, were monitored by infrared spectroscopy.

RESULTS

In E. coli, most of the changes occurred on proteins and lipids, suggesting a key effect on lipopolysaccharides in the first irradiation times. In S. warneri, proteins were the major molecular targets of oxidative damage but phospholipids and polysaccharides were also affected.

CONCLUSION

Infrared spectroscopy is a very interesting tool to monitor biochemical changes induced by photosensitization in bacteria and also to infer on its mechanism of action.

Mechanism and In Vivo Evaluation: Photodynamic Antibacterial Chemotherapy of Lysine-Porphyrin Conjugate

Lysine-porphyrin conjugate 4i has potent photosensitive antibacterial effect on clinical isolated bacterial strains such as Methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, and Pseudomonas aeruginosa. The mechanism of photodynamic antibacterial chemotherapy of 4i (4i-PACT) in vitro and the treatment effect in vivo was investigated in this paper. Atomic force microscopy (AFM) revealed that 4i-PACT can effectively destroy membrane and wall of bacteria, resulting in leakage of its content. This was confirmed by dual fluorescent staining with acridine orange/ethidium bromide and measuring materials absorption at 260 nm. Agarose gel electrophoresis measurement showed that 4i-PACT can damage genomic DNA. Healing of wound in rat infected by mixed bacteria showed that the efficiency of 4i-PACT is dependent on the dose of light. These results showed that 4i-PACT has promising bactericidal effect both in vitro and in vivo.

Enhancement of photodynamic inactivation against Pseudomonas aeruginosa by a nano-carrier approach

As pathogens steadily develop resistance to widely used antibiotics, new methodologies for their efficient inactivation must be developed. Photodynamic therapy is an upcoming technique that provides an alternative option for treating pathogenic infections. The efficiency of photodynamic therapy has been limited by the use of aqueous mediums for dispersing photosensitising agents. Toluidine Blue O (TBO) was chosen for this study as a cationic photosensitiser to inhibit Gram-negative bacterium Pseudomonas aeruginosa. Enhanced delivery of the photosensitiser was ensured by utilising an essential oil-based microemulsion. The efficiency of photodynamic therapy was further improved by the use of a chemical penetration enhancer to improve permeability of the bacterial outer membrane. TBO accumulation patterns in neonate pig skin were studied using confocal laser scanning microscopy. The physicochemical properties of the TBO loaded microemulsion, including UV-vis absorbance, size distribution and zeta potential, were analysed to understand the enhanced antimicrobial activity. Confocal laser scanning microscopy confirmed the formation of a TBO reservoir in the skin by the TBO-loaded microemulsions. TBO (5 μg/mL) in the vehicles significantly inhibited the growth of P. aeruginosa. All these efforts resulted in inhibition obtained at a drug concentration and light intensity much lower than what is reported by the works of previous investigators.

Effects of photodynamic therapy on Enterococcus faecalis biofilms

Microbial biofilms are involved in almost all infectious pathologies of the oral cavity. This has led to the search for novel therapies specifically aimed at biofilm elimination. In this study, we used atomic force microscopy (AFM) to visualize injuries and to determine surface roughness, as well as confocal laser scanning microscopy (CLSM) to enumerate live and dead bacterial cells, to determine the effects of photodynamic therapy (PDT) on Enterococcus faecalis biofilms. The AFM images showed that PDT consisting of methylene blue and a 670-nm diode laser (output power 280 mW during 30 s) or toluidine blue and a 628-nm LED light (output power 1000 mW during 30 s) induced severe damage, including cell lysis, to E. faecalis biofilms, with the former also causing an important increase in surface roughness. These observations were confirmed by the increase in dead cells determined using CLSM. Our results highlight the potential of PDT as a promising method to achieve successful oral disinfection.

In Vitro Evaluation of Antimicrobial Photodynamic Therapy Associated with Hydroalcoholic Extracts of Schinopsis brasiliensis Engl.: New Therapeutic Perspectives

OBJECTIVE

The aim of this study was to evaluate the photodynamic potential of extracts of Schinopsis brasiliensis Engl. on bacteria involved in several human infections.

BACKGROUND DATA

Photodynamic therapy (PDT) involves the interaction of light with an appropriate and photosensitizer wavelength, and the prospect of existing photosensitive compounds in herbal extracts enhanced by the application of laser diode has been promising.

METHODS

The antibacterial activity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Enterococcus faecalis was obtained by the disk diffusion method on agar. The laser diode InGaAIP was used with 660 nm wavelength, 100 mW, and 4 J/cm(2), and the application was performed in a timely manner for 34 sec on each disk tested. The groups tested were: Laser and bark extract (B+L+); bark extract only (B+L-); Laser and leaf extract (F+L+); leaf extract only (F+L-); Laser and malachite green (M+L+); malachite green only (M+L-); and laser only (L+).

RESULTS

There were significant differences between the B+L- and B+L+ groups (p=0.029) and between the L+F- and L+F+ groups (p=0.029) at various concentrations of the nebulized extracts of bark and leaf. Among the tested pathogens, S. aureus showed the highest zone of inhibition, 24.55±0.36 mm in group B+L+, 500 mg.mL(-1).

CONCLUSIONS

PDT with malachite green was effective, and groups B+L+ and F+L+ showed excellent activity on the bacteria tested, suggesting the presence of photosensitizers in extracts of S. brasiliensis Engl.

Atomic force microscopy visualization of injuries in Enterococcus faecalis surface caused by Er,Cr:YSGG and diode lasers

Aim: To visualize by Atomic Force Microscopy the alterations induced on Enterococcus. faecalis surface after treatment with 2 types of laser: Erbium chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser and Diode laser. Material and Methods: Bacterial suspensions from overnight cultures of E. faecalis were irradiated during 30 seconds with the laser-lights at 1 W and 2 W of power, leaving one untreated sample as control. Surface alterations on treated E. faecalis were visualized by Atomic Force Microscopy (AFM) and its surface roughness determined. Results: AFM imaging showed that at high potency of laser both cell morphology and surface roughness resulted altered, and that several cell lysis signs were easily visualized. Surface roughness clearly increase after the treatment with Er,Cr:YSGG at 2W of power, while the other treatments gave similar values of surface roughness. The effect of lasers on bacterial surfaces visualized by AFM revealed drastic alterations. Conclusions: AFM is a good tool to evaluate surface injuries after laser treatment; and could constitute a measure of antimicrobial effect that can complete data obtained by determination of microbial viability.

Key words:Atomic force microscopy, Er,Cr:YSGG laser, diode laser, Enterococcus faecalis, surface roughness.

Manual and Rotary Instrumentation Ability to Reduce Enterococcus faecalis Associated with Photodynamic Therapy in Deciduous Molars

This aim of this study was to assess the ability of manual or rotary instrumentation associated with photodynamic therapy (PDT) to reduce Enterococcus faecalis using three combinations of light/photosensitizers: toluidine blue O/laser, fuchsin/halogen light and fuchsin/LED. Twenty deciduous molars were selected and contaminated with Enterococcus faecalis (McFarland 0.5 scale). Working length determination was performed by visual method. The teeth were randomly divided into two groups: G1 (n=10): manual instrumentation (Kerr-type files) and G2 (n=10): rotary instrumentation (ProTaper system). The bacteria were collected three times using sterile paper cones compatible with the anatomic diameter of the root canal for 30 s before and after instrumentation and after PDT. The samples were diluted in peptone water, seeded on blood agar plates and incubated in an oven at 37 °C for colony-forming units counting. The decrease of E. faecalis counts after instrumentation and after PDT was compared using the Wilcoxon test, t-test and Kruskal Wallis test. A significant reduction of E. faecalis occurred after manual and rotary instrumentation and after PDT using the three combinations of light/photosensitizer (p<0.05). It may be concluded that both rotary and manual instrumentation reduced E. faecalis. Fuchsin with halogen light or LED irradiation and toluidine blue O with laser irradiation can be used to reduce E. faecalis in root canals of primary molars. PDT can be used as an adjuvant to conventional endodontic treatment.

An insight on bacterial cellular targets of photodynamic inactivation

The emergence of microbial resistance is becoming a global problem in clinical and environmental areas. As such, the development of drugs with novel modes of action will be vital to meet the threats created by the rise in microbial resistance. Microbial photodynamic inactivation is receiving considerable attention for its potentialities as a new antimicrobial treatment. This review addresses the interactions between photosensitizers and bacterial cells (binding site and cellular localization), the ultrastructural, morphological and functional changes observed at initial stages and during the course of photodynamic inactivation, the oxidative alterations in specific molecular targets, and a possible development of resistance.

N, N'-Olefin functionalized bis-imidazolium gold(I) salt is an efficient candidate to control keratitis-associated eye infection

Keratitis treatment has become more complicated due to the emergence of bacterial or fungal pathogens with enhanced antibiotic resistance. The pharmaceutical applications of N-heterocyclic carbene complexes have received remarkable attention due to their antimicrobial properties. In this paper, the new precursor, 3,3′-(p-phenylenedimethylene) bis{1-(2- methyl-allyl)imidazolium} bromide (1a) and its analogous PF₆ salt (1b) were synthesized. Furthermore, silver(I) and gold(I) -N-heterocyclic carbene (NHC) complexes [Ag₂LBr₂/Au₂LBr₂; 2a/3a], [(Ag₂L₂)(PF₆)₂/(Au₂L₂)(PF₆)₂; 2b/3b] were developed from their corresponding ligands. All compounds were screened for their antimicrobial activities against multiple keratitis-associated human eye pathogens, including bacteria and fungi. Complexes 2a and 3a showed highest activity, and the effectiveness of 3a was also studied, focusing eradication of pathogen biofilm. Furthermore, the structures of 1a, 2a and 3b were determined using single crystal X-ray analysis, 2b and 3a were optimized theoretically. The mechanism of action of 3a was evaluated by scanning electron microscopy and docking experiments, suggesting that its target is the cell membrane. In summary, 3a may be helpful in developing antimicrobial therapies in patients suffering from keratitis-associated eye infections caused by multidrug-resistant pathogens.

AFM probing the mechanism of synergistic effects of the green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) with cefotaxime against extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli

Background

Extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae poses serious challenges to clinicians because of its resistance to many classes of antibiotics.

Methods and Findings

The mechanism of synergistic activity of a combination of (−)-epigallocatechin-3-gallate (EGCG) and β-lactam antibiotics cefotaxime was studied on Extended-spectrum β-lactamase producing Escherichia coli (ESBL-EC), by visualizing the morphological alteration on the cell wall induced by the combination using atomic force microscopy (AFM). Cells at sub-MICs (sub-minimum inhibitory concentrations) of cefotaxime were initially filamentated but recovered to the normal shape later, whereas cells at sub-MICs of EGCG experienced temporal disturbance on the cell wall such as leakage and release of cellular debris and groove formation, but later recovered to the normal shape. In contrast, the combination of cefotaxime and EGCG at their respective sub-MICs induced permanent cellular damages as well as continuous elongation in cells and eventually killed them. Flow cytometry showed that intracellular oxidative stress levels in the cell treated with a combination of EGCG and cefotaxime at sub-MICs were higher than those in the cells treated with either cefotaxime or EGCG at sub-MICs.

Conclusions

These results suggest that the synergistic effect of EGCG between EGCG and cefotaxime against ESBL-EC is related to cooperative activity of exogenous and endogenous reactive oxygen species (ROS) generated by EGCG and cefotaxime, respectively.

Photodynamic inactivation of methylene blue and tungsten-halogen lamp light against food pathogen Listeria monocytogenes

The aim of this study was to verify the bactericidal effect and the damage of photodynamic inactivation (PDI) using methylene blue (MB) and tungsten-halogen lamp over Listeria monocytogenes via atomic force microscopy, absorption spectrophotometry, agarose gel electrophoresis, real-time PCR and SDS-PAGE. The obtained data indicated that the viability of L. monocytogenes was ca 7-log reduced by illumination with 10 min tungsten-halogen lamp light under the presence of 0.5 μg mL(-1) MB, and this bactericidal activity against L. monocytogenes of PDI increased proportionally to the concentration of MB and the duration of irradiation. Moreover, after irradiation with MB and visible light, the leakage of intracellular contents was estimated by spectrophotometer at OD(260) and OD(280), which correlated with morphological alterations. Furthermore, genomic DNA cleavage and protein degradation were also detected after PDI treatment. Consequently, breakage of the membrane, damage of the genomic DNA and degradation of bacterial proteins may play an important role in the mechanisms involved in PDI-MB bactericidal activity on L. monocytogenes.

Reducing Vibrio load in Artemia nauplii using antimicrobial photodynamic therapy: a promising strategy to reduce antibiotic application in shrimp larviculture

We propose antimicrobial photodynamic therapy (aPDT) as an alternative strategy to reduce the use of antibiotics in shrimp larviculture systems. The growth of a multiple antibiotic resistant Vibrio harveyi strain was effectively controlled by treating the cells with Rose Bengal and photosensitizing for 30 min using a halogen lamp. This resulted in the death of > 50% of the cells within the first 10 min of exposure and the 50% reduction in the cell wall integrity after 30 min could be attributed to the destruction of outer membrane protein of V. harveyi by reactive oxygen intermediates produced during the photosensitization. Further, mesocosm experiments with V. harveyi and Artemia nauplii demonstrated that in 30 min, the aPDT could kill 78.9% and 91.2% of heterotrophic bacterial and Vibrio population respectively. In conclusion, the study demonstrated that aPDT with its rapid action and as yet unreported resistance development possibilities could be a propitious strategy to reduce the use of antibiotics in shrimp larviculture systems and thereby, avoid their hazardous effects on human health and the ecosystem at large.

AFM study of the differential inhibitory effects of the green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) against Gram-positive and Gram-negative bacteria

(-)-Epigallocatechin-3-gallate (EGCG), a main constituent of tea catechins, affects Gram-positive and Gram-negative bacteria differently; however, the underlying mechanisms are not clearly understood. Atomic force microscopy (AFM) was used to compare morphological alterations in Gram-positive and Gram-negative bacteria induced by EGCG and by H(2)O(2) at sub-minimum inhibitory concentrations (MICs). EGCG initially induced aggregates in the cell envelopes of Staphylococcus aureus and eventually caused cell lysis, which was not observed in cells treated with H(2)O(2). It initially induced nanoscale perforations or microscale grooves in the cell envelopes of Escherichia coli O157:H7 which eventually disappeared, similar to E. coli cells treated with H(2)O(2). An E. coli O157:H7 tpx mutant, with a defect in thioredoxin-dependent thiol peroxidase (Tpx), was more severely damaged by EGCG when compared with its wild type. Similar differing effects were observed in other Gram-positive and Gram-negative bacteria when exposed to EGCG; it caused aggregated in Streptococcus mutans, while it caused grooves in Pseudomonas aeruginosa. AFM results suggest that the major morphological changes of Gram-negative bacterial cell walls induced by EGCG depend on H(2)O(2) release. This is not the case for Gram-positive bacteria. Oxidative stress in Gram-negative bacteria induced by EGCG was confirmed by flow cytometry.

Optimization of fixation methods for observation of bacterial cell morphology and surface ultrastructures by atomic force microscopy

Fixation ability of five common fixation solutions, including 2.5% glutaraldehyde, 10% formalin, 4% paraformaldehyde, methanol/acetone (1:1), and ethanol/acetic acid (3:1) were evaluated by using atomic force microscopy in the present study. Three model bacteria, i.e., Escherichia coli, Pseudomonas putida, and Bacillus subtilis were applied to observe the above fixation methods for the morphology preservation of bacterial cells and surface ultrastructures. All the fixation methods could effectively preserve cell morphology. However, for preserving bacterial surface ultrastructures, the methods applying aldehyde fixations performed much better than those using alcohols, since the alcohols could detach the surface filaments (i.e., flagella and pili) significantly. Based on the quantitative and qualitative assessments, the 2.5% glutaraldehyde was proposed as a promising fixation solution both for observing morphology of both bacterial cell and surface ultrastructures, while the methonal/acetone mixture was the worst fixation solution which may obtain unreliable results.

Application of AFM from microbial cell to biofilm

Atomic Force Microscopy (AFM) has proven itself over recent years as an essential tool for the analysis of microbial systems. This article will review how AFM has been used to study microbial systems to provide unique insight into their behavior and relationship with their environment. Immobilization of live cells has enabled AFM imaging and force measurement to provide understanding of the structure and function of numerous microbial cells. At the macromolecular level AFM investigation into the properties of surface macromolecules and the energies associated with their mechanical conformation and functionality has helped unravel the complex interactions of microbial cells. At the level of the whole cell AFM has provided an integrated analysis of how the microbial cell exploits its environment through its selective, adaptable interface, the cell surface. In addition to these areas of study the AFM investigation of microbial biofilms has been vital for industrial and medical process analysis. There exists a tremendous potential for the future application of AFM to microbial systems and this has been strengthened by the trend to use AFM in combination with other characterization methods, such as confocal microscopy and Raman spectroscopy, to elucidate dynamic cellular processes.

Photodynamic treatment: a new efficient alternative for surface sanitation

A novel and promising technology-photodynamic treatment (PDT), aimed for surface cleaning and sanitation in food industry-is presented. It is based on the treatment of surfaces with nontoxic dyes (photosensitizers), followed by illumination of the surface with regular white light. The method is currently used in the medical field and was proved to have wide specificity against a variety of bacterial and viral pathogens as well as against yeasts and protozoa. An additional advantage of this approach is that development of resistance of microorganisms to PDT was shown to be unlikely. The theoretical basis of light-induced antimicrobial treatment is described, followed by examples of its application for the cleaning and disinfection of surfaces. All available information supports the idea that PDT could offer a very efficient and cost-effective way to combat microbial contamination of foods. The advantages and pitfalls of the technique are discussed. Directions of future research needed for bringing the technology to commercial reality are identified.