Eradication of Acinetobacter baumannii by photosensitized agents in vitro

Antimicrobial photodynamic therapy against oral biofilm: influencing factors, mechanisms, and combined actions with other strategies

Oral biofilms are a prominent cause of a wide variety of oral infectious diseases which are still considered as growing public health problems worldwide. Oral biofilms harbor specific virulence factors that would aggravate the infectious process and present resistance to some traditional therapies. Antimicrobial photodynamic therapy (aPDT) has been proposed as a potential approach to eliminate oral biofilms via in situ-generated reactive oxygen species. Although numerous types of research have investigated the effectiveness of aPDT, few review articles have listed the antimicrobial mechanisms of aPDT on oral biofilms and new methods to improve the efficiency of aPDT. The review aims to summarize the virulence factors of oral biofilms, the progress of aPDT in various oral biofilm elimination, the mechanism mediated by aPDT, and combinatorial approaches of aPDT with other traditional agents.

Priming effect with photoinactivation against extensively drug-resistant Enterobacter cloacae and Klebsiella pneumoniae

In this study, we present antimicrobial blue light (aBL) and antimicrobial photoinactivation with green light in the presence of Rose Bengal (aPDI) to modulate the susceptibility of extensively drug-resistant (XDR) Enterobacter cloacae and Klebsiella pneumoniae clinical isolates to antimicrobials. This process can be considered a photodynamic priming tool that influences other therapeutic options, such as antibiotics. The current study evaluated the different environments to estimate the most effective priming conditions by testing a broad spectrum of antimicrobials (including antimicrobials with different targets and mechanisms of action). The susceptibility of the E. cloacae and K. pneumoniae clinical isolates to various antibiotics after aBL and green light (with rose bengal) as aPDI treatment was examined with multiple methods of synergy testing (e.g., diffusion methods, checkerboard assay, postantibiotic effect), and most effective photoinactivation conditions were implemented for each environment. When Enterobacteriaceae were exposed to aBL, the most efficient reduction in survival rate under TSB conditions was observed. Similar results were observed when rose bengal, as a photosensitizer, was present during the exposure to green light in PBS. aBL and aPDI led to an increased susceptibility of K. pneumoniae and E. cloacae isolates to chloramphenicol and colistin or fosfomycin and colistin antibiotics, respectively. However, among the 4 tested isolates, we observed synergies between different antimicrobial agents and photoinactivation conditions. Thus, it may suggest that the sensitization process may be considered a strain dependent priming tool.

Charge effect of water-soluble porphyrin derivatives as a prototype to fight infections caused by Acinetobacter baumannii by aPDT approaches

In the last decade, Acinetobacter baumannii has emerged as a pathogen associated with infections in intensive care units worldwide, especially due to its ability to resist an extensive list of antibiotics. In this context, porphyrins have emerged as an important strategy in photodynamic therapy, since they are a group of tetrapyrrolic compounds with important photochemical and photobiological activities. In this study, the antimicrobial photodynamic activity of meso-tetra(4-N-methyl-pyridyl)porphyrin (H₂TMePyP⁺) and meso-tetra(4-sulfonatophenyl)porphyrin (H₂TPPS^‒) was evaluated against A. baumannii by minimum inhibitory concentration (MIC), anti-biofilm activity, and the interaction with antibiotics after exposure to white-light LED irradiation. The cationic derivative H₂TMePyP⁺ was more potent (MIC = 0.61 µM) than H₂TPPS^‒, with anti-biofilm activity and increased the antimicrobial activity of ciprofloxacin and amikacin. Given these findings, the tetra-cationic porphyrins can be assumed as prototypes to optimize and develop new agents by promoting oxidative stress and inducing free radical production.

Photodynamic and antibiotic therapy in combination against bacterial infections: efficacy, determinants, mechanisms, and future perspectives

Antibiotic treatment, the mainstay for the control of bacterial infections, is greatly hampered by the global prevalence of multidrug-resistant (MDR) bacteria. Photodynamic therapy (PDT) is effective against MDR infections, but PDT-induced bacterial inactivation is often incomplete, causing the relapse of infections. Combination of PDT and antibiotics is a promising strategy to overcome the limitation of both antibiotic treatment and PDT, exerting increased disinfection efficacy on MDR bacterial pathogens versus either of the monotherapies alone. In this review, we present an overview of the therapeutic effects of PDT/antibiotic combinations that have been developed. We further summarize the influencing factors and the governing molecular mechanisms of the therapeutic outcomes of PDT/antibiotic combinations. In the end, we provide concluding remarks on the strengths, limitations, and future research directions of PDT/antibiotic combination therapy to guide its appropriate usage and further development.

Factors Determining the Susceptibility of Bacteria to Antibacterial Photodynamic Inactivation

Photodynamic inactivation of microorganisms (aPDI) is an excellent method to destroy antibiotic-resistant microbial isolates. The use of an exogenous photosensitizer or irradiation of microbial cells already equipped with endogenous photosensitizers makes aPDI a convenient tool for treating the infections whenever technical light delivery is possible. Currently, aPDI research carried out on a vast repertoire of depending on the photosensitizer used, the target microorganism, and the light delivery system shows efficacy mostly on in vitro models. The search for mechanisms underlying different responses to photodynamic inactivation of microorganisms is an essential issue in aPDI because one niche (e.g., infection site in a human body) may have bacterial subpopulations that will exhibit different susceptibility. Rapidly growing bacteria are probably more susceptible to aPDI than persister cells. Some subpopulations can produce more antioxidant enzymes or have better performance due to efficient efflux pumps. The ultimate goal was and still is to identify and characterize molecular features that drive the efficacy of antimicrobial photodynamic inactivation. To this end, we examined several genetic and biochemical characteristics, including the presence of individual genetic elements, protein activity, cell membrane content and its physical properties, the localization of the photosensitizer, with the result that some of them are important and others do not appear to play a crucial role in the process of aPDI. In the review, we would like to provide an overview of the factors studied so far in our group and others that contributed to the aPDI process at the cellular level. We want to challenge the question, is there a general pattern of molecular characterization of aPDI effectiveness? Or is it more likely that a photosensitizer-specific pattern of molecular characteristics of aPDI efficacy will occur?

Pentamidine enhances photosensitization of Acinetobacter baumannii using diode lasers with emission of light at wavelength of ʎ = 405 nm and ʎ = 635 nm

Antimicrobial photodynamic inactivation is currently one of the most promising trends in the modern bactericidal protocols. Under the conditions defined in our studies, we found that in vitro photosensitization of A. baumannii with 5-ALA as a precursor of protoporphyrin IX (photosensitizer) reduces the concentration of viable cells in planktonic cultures, and this process can be strongly enhanced by pentamidine. Diode lasers with the peak-power wavelength of ʎ = 405 nm (radiation intensity of 26 mW cm^-2) and ʎ = 635 nm (radiation intensity of 55 mW cm^-2) were used in this study. It was found that a blue laser light (energy fluence of 64 J cm^-2; no external photosensitizer) in the presence of pentamidine resulted in a reduction of CFU of 99.992 % compared to 99.97 % killing without pentamidine. When a red laser light was used in the experiments (energy fluence of 136 J cm^-2; no external photosensitizer), the mortality rate was 99.98 % in the presence of pentamidine compared to 99.93 % of those killed without the addition of this drug. The lethal effect with 5-ALA was achieved under blue light fluence of 16 J cm^-2 (in the presence of pentamidine) and 32 J cm^-2 (without pentamidine). In the case of laser light of 635 nm, the lethal effect with 5-ALA was attained with energy fluence of 51 J cm^-2 (with pentamidine) and 102 J cm^-2 (without pentamidine). The possible roles of pentamidine in enhancing photodynamic inactivation of A. baumannii have been discussed.

Antibacterial Photoactivity and Thermal Stability of Tetra-cationic Porphyrins Immobilized on Cellulosic Fabrics

The thermal stability and photo-bactericidal effect of several tetra-cationic porphyrins and their zinc ion compounds immobilized onto cellulosic fabrics against S. aureus, P. aeruginosa, and E. coli were investigated and compared using a 100 W tungsten lamp. Immobilization of various concentrations of these photosensitizers onto cellulosic fabrics was carried out and characterized by ATR-FT-IR, DRS, TGA, and SEM. Applied cellulosic fabrics with the photosensitizers exhibited remarkable photo-stability, thermal stability, and antimicrobial activity against these studied strains.

Antibacterial activity of Cu(II) and Co(II) porphyrins: role of ligand modification

In this study, we report antibacterial activity of metalloporphyrins; 5, 10, 15, 20-tetrakis (para-X phenyl)porphyrinato M (II) [where X = H, NH₂ and COOMe for M = Cu and X = COOH  and OMe for M = Co]. The activity study of the as-synthesized metalloporphyrins toward two Gram-positive (S. aureus and S. pyogenes) and two Gram-negative (E. coli and K. pneumoniae) bacteria showed a promising inhibitory activity. Among the complexes under study, the highest antibacterial activity is observed for 5, 10, 15, 20-tetrakis (p-carboxyphenyl)porphyrinato cobalt (II), with inhibition zone of 16.5 mm against Staphylococcus aureus (S. aureus). This activity could be attributed to the high binding ability of COOH group to cellular components, membranes, proteins, and DNA as well as the lipophilicity of the complex. Moreover, consistent with literature report, the study revealed that metalloporphyrins with electron withdrawing group at para-positions have better antibacterial activity than metalloporphyrin which possess electron donating group at para position.

Antimicrobials Are a Photodynamic Inactivation Adjuvant for the Eradication of Extensively Drug-Resistant Acinetobacter baumannii

The worldwide emergence of extensively drug resistant (XDR) Acinetobacter baumannii has reduced the number of antimicrobials that exert high bactericidal activity against this pathogen. This is the reason why many scientists are focusing on investigations concerning novel non-antibiotic strategies such as antimicrobial photodynamic inactivation (aPDI) or the use of antimicrobial blue light (aBL). Therefore, the aim of the current study was to screen for antimicrobial synergies of routinely used antibiotics and phototherapies, including both aPDI involving exogenously administered photosensitizing molecules, namely, rose bengal, and aBL, involving excitation of endogenously produced photoactive compounds. The synergy testing was performed in accordance with antimicrobial susceptibility testing (AST) standards, including various methodological approaches, i.e., antibiotic diffusion tests, checkerboard assays, CFU counting and the evaluation of postantibiotic effects (PAEs). We report that combining antimicrobials and aPDI/aBL treatment led to a new strategy that overcomes drug resistance in XDR A. baumannii, rendering this pathogen susceptible to various categories of antibiotics. Sublethal aPDI/aBL treatment in the presence of sub-MIC levels of antimicrobials effectively killed A. baumannii expressing drug resistance to studied antibiotics when treated with only antibiotic therapy. The susceptibility of XDR A. baumannii to a range of antibiotics was enhanced following sublethal aPDI/aBL. Furthermore, 3′-(p-aminophenyl) fluorescein (APF) testing indicated that significantly increased reactive oxygen species production upon combined treatment could explain the observed synergistic activity. This result represents a conclusive example of the synergistic activity between photodynamic inactivation and clinically used antimicrobials leading to effective eradication of XDR A. baumannii isolates and indicates a potent novel therapeutic approach.

Polymyxin Derivatives that Sensitize Gram-Negative Bacteria to Other Antibiotics

Polymyxins (polymyxin B (PMB) and polymyxin E (colistin)) are cyclic lipodecapeptide antibiotics, highly basic due to five free amino groups, and rapidly bactericidal against Gram-negative bacteria, such as the majority of Enterobacteriaceae as well as Acinetobacter baumannii and Pseudomonas aeruginosa. Their clinical use was abandoned in the 1960s because of nephrotoxicity and because better-tolerated drugs belonging to other antibiotic classes were introduced. Now, due to the global dissemination of extremely-drug resistant Gram-negative bacterial strains, polymyxins have resurged as the last-line drugs against those strains. Novel derivatives that are less toxic and/or more effective at tolerable doses are currently under preclinical development and their properties have recently been described in several extensive reviews. Other derivatives lack any direct bactericidal activity but damage the outermost permeability barrier, the outer membrane, of the target bacteria and make it more permeable to many other antibiotics. This review describes the properties of three thus far best-characterized “permeabilizer” derivatives, i.e., the classic permeabilizer polymyxin B nonapeptide (PMBN), NAB7061, and SPR741/NAB741, a compound that recently successfully passed the clinical phase 1. Also, a few other permeabilizer compounds are brought up.

The Photodynamic Effect of Tetra-Substituted N-Methyl-Pyridyl-Porphine Combined with the Action of Vancomycin or Host Defense Mechanisms Disrupts Staphylococcus Epidermidis Biofilms

The skin commensal and opportunistic pathogen Staphylococcus epidermidis is an important cause of nosocomial infections. Virulence is attributable to formation of biofilm, which provides a microenvironment that protects the bacterium from attack by the host immune system and by chemotherapy. In this study we extended to S. epidermidis strategies previously aimed at treatment of S. aureus bio films using photodynamic treatment (PDT) combined with chemotherapy or phagocytosis. A significant reduction in bacterial survival was observed when structurally distinct biofilms were exposed to the cationic porphyrin, tetra-substituted N-methyl-pyridyl-porphine (TMP), and simultaneously to visible light. Of note, the extent of biofilm clearance depended on its maturation stage: developing, young biofilms, were more sensitive towards PDT than mature biofilms. Furthermore, PDT-treated biofilms exposed to vancomycin or subjected to phagocytic action of whole blood were almost completely eradicated. The data we obtained establish that PDT combined with antibiotics or host defenses may also be a useful approach for the inactivation of S. epidermidis biofilms.

Development of a practical animal model of photodynamic therapy using a high concentration of extracellular talaporfin sodium in interstitial fluid: influence of albumin animal species on myocardial cell photocytotoxicity in vitro

Photodynamic reaction-induced photocytotoxicity using talaporfin sodium is inhibited by serum proteins binding to talaporfin sodium. The serum albumin binding site for talaporfin sodium differs among animal species. To identify a practical animal therapeutic model, we studied the ability of human, canine, bovine, and porcine albumin to influence talaporfin sodium-induced photocytotoxicity in rat myocardial cells in vitro. Human, canine, bovine, and porcine serum albumins were used. The ratio of talaporfin sodium binding, which is strongly associated with photocytotoxicity, was measured by ultrafiltration with an albumin concentration of 0.5-20 mg/ml and 20 μg/ml talaporfin sodium to mimic interstitial fluid. Rat myocardial cell lethality was measured by the WST assay 2 h after samples were exposed to a radiant exposure of 20 J/cm² by a red diode laser (Optical Fuel™, Sony, Tokyo, Japan) with a wavelength of 663 nm. The binding ratio dependence on albumin concentration differed among the animal species. Bovine albumin exhibited the largest difference from human albumin, with a maximum difference of 31% at 2 mg/ml albumin. The cell lethality characteristic was similar between human and canine albumin. The cell lethality dependence on albumin was not in the same order as the binding ratio. Cell lethality was lowest for human albumin with higher albumin concentrations between 5 and 20 mg/ml. There were no significant differences in cell lethality between bovine and porcine albumin and between human and canine albumin. We suggest that the canine model may be a useful animal therapeutic model for evaluating photodynamic therapy using a high concentration of the photosensitizer in the extracellular space.

Membrane Oxidation in Cell Delivery and Cell Killing Applications

Cell delivery or cell killing processes often involve the crossing or disruption of cellular membranes. We review how, by modifying the composition and properties of membranes, membrane oxidation can be exploited to enhance the delivery of macromolecular cargoes into live human cells. We also describe how membrane oxidation can be utilized to achieve efficient killing of bacteria by antimicrobial peptides. Finally, we present recent evidence highlighting how membrane oxidation is intimately engaged in natural biological processes such as antigen delivery in dendritic cells and in the killing of bacteria by antimicrobial peptides. Overall, the insights that have been recently gained in this area should facilitate the development of more effective delivery technologies and antimicrobial therapeutic approaches.

Modulation of virulence in Acinetobacter baumannii cells surviving photodynamic treatment with toluidine blue

INTRODUCTION

Widespread resistance to antimicrobial agents has led to a dearth of therapeutic choices in treating Acinetobacter baumannii infections, leading to new strategies for treatment being needed. We evaluated the effects of photodynamic therapy (PDT) as an alternative antimicrobial modality on the virulence features of cell-surviving PDT.

MATERIALS AND METHODS

To determine the sublethal PDT (sPDT), a colistin-resistant, extensively drug-resistant A. baumannii (CR-XDR-AB) clinical isolate and A. baumannii and ATCC 19606 strains, photosensitized with toluidine blue O (TBO), were irradiated with light emitting diodes, following bacterial viability measurements. The biofilm formation ability, outer membrane (OM) integrity, and antimicrobial susceptibility profiles were assessed for cell-surviving PDT. The effects of sPDT on the expression of virulent genes were evaluated by real-time quantitative reverse transcription PCR (qRT-PCR).

RESULTS

sPDT resulted in the reduction of the biofilm formation capacity, and its metabolic activity in strains. The OM permeability and efflux pump inhibition of the sPDT-treated CR-XDR-AB cells were increased; however, there was no significant change in OM integrity in ATCC 19606 strain after sPDT. sPDT reduced the minimum inhibitory concentrations of the most tested antimicrobials by ≥2-fold in CR-XDR-AB. lpsB, blsA, and dnaK were upregulated after the strains were treated with sPDT; however, a reduction in the expression of csuE, epsA, and abaI was observed in the treated strains after sPDT.

CONCLUSION

The susceptibility of CR-XDR-AB to a range of antibiotics was enhanced following sPDT. The virulence of strains is reduced in cells surviving PDT with TBO, and this may have potential implications of PDT for the treatment of A. baumannii infections.

Particle-based photodynamic therapy based on indocyanine green modified plasmonic nanostructures for inactivation of a Crohn's disease-associated Escherichia coli strain

Particle-based photodynamic therapy (PPDT) holds great promise in theranostic applications. Herein, we demonstrate that PPDT based on gold nanorods coated with an indocyanine green (ICG)-loaded silica shell allows for the inactivation of the Crohn's disease-associated adherent-invasive Escherichia coli strain LF82 (E. coli LF82) under pulsed laser light irradiation at 810 nm. Fine-tuning of the plasmonic structures together with maximizing the photosensitizer loading onto the nanostructures allowed optimizing the singlet oxygen generation capability and the PPDT efficiency. Using a nanoparticle concentration low enough to suppress photothermal heating effects, 6 log10 reduction in E. coli LF82 viability could be achieved using gold nanostructures displaying a plasmonic band at 900 nm. An additional modality of nanoparticle-based photoinactivation of E. coli is partly observed, with 3 log10 reduction of bacterial viability using Au NRs@SiO2 without ICG, due to the two-photon induced formation of reactive oxygen species. Interaction of the particles with the bacterial surface, responsible for the disruption of the bacterial integrity, together with the generation of moderate quantities of singlet oxygen could account for this behavior.

Effects of divalent cations, EDTA and chitosan on the uptake and photoinactivation of Escherichia coli mediated by cationic and anionic porphyrins

The effect of divalent cations, EDTA and chitosan (CS) on the uptake and photoinactivation of Escherichia coli produced by 5,10,15,20-tetrakis(4-N,N,N-trimethylammoniumphenyl)porphyrin (TMAP(4+)), 5,10-di(4-methylphenyl)-15,20-di(4-N,N,N-trimethylammoniumphenyl)porphyrin (MPAP(2+)) and 5,10,15,20-tetra(4-sulphonatophenyl)porphyrin (TPPS(4-)) were examined under different conditions. These porphyrins were rapidly bound to E. coli cells (<2.5min) and the uptake of photosensitizers was not dependent on incubation temperature, reaching values of 0.61, 0.18 and 0.08nmol/10(8) cells for TMAP(4+), MPAP(2+) and TPPS(4-), respectively. The addition of Ca(2+) or Mg(2+) to the cultures enhanced the uptake of MPAP(2+) and TPPS(4-) by cells. In contrast, the amount of TMAP(4+) bound to cells was decreased. The presence of EDTA produced an increase in the uptake of porphyrins by cells, while CS mainly enhanced the amount of TPPS(4-) bound to E. coli. The photoinactivation of E. coli cells mediated by TMAP(4+) was highly effective even at low concentration (1μM) and short irradiation period (5min). However, a reduction in the phototoxicity was found for TMAP(4+) in presence of Ca(2+) and Mg(2+). In contrast, the phototoxic activity mediated by MPAP(2+) and TPPS(4-) was increased. Addition of EDTA did not show effect on the photoinactivation induced by cationic porphyrins, while a small enhance was found for TPPS(4-). Moreover, inactivation of E. coli cells was achieved in the presence CS. This cationic polymer was antimicrobial by itself in the dark. Using a slightly toxic CS concentration, the phototoxic activity induced by TMAP(4+) was diminished. This effect was mainly observed at lower concentration of TMAP(4+) (0.5-1μM). In contrast, an increase in E. coli photoinactivation was obtained for MPAP(2+) and TPPS(4-) in presence of CS. Thus, this natural polymeric destabilizer agent mainly benefited the photoinactivation mediated by TPPS(4-).

Antibacterial effects of the tellurium compound OTD on E. coli isolates

The antibacterial effects of a new organo-tellurium compound [Octa-O-bis-(R,R)-tartarate ditellurane (OTD)] on Escherichia coli isolates as a model are shown. OTD was found to be a bactericidal drug. It exhibits inhibition zones on a protein-rich agar medium but not in a protein-poor medium unless a thiol is added. When applied at the lag phase, OTD inhibits more efficiently than at the log phase. Thiols enhance the efficiency at the log phase. OTD inhibits biofilm formation of E. coli. X-ray microanalysis demonstrated damage caused to the Na⁺/K⁺ pumps and leakage of potassium and phosphorous. Scanning electron microscopy demonstrated an incomplete surface of the bacterial cell wall with a concavity in the center that looks like a hole. Transmission electron microscopy demonstrated severe damage, such as depletion, perforation, and holes in the inner membrane. These results indicate for the first time that the new tellurium compound has antibacterial activities.

Antimicrobial photodynamic therapy with decacationic monoadducts and bisadducts of [70]fullerene: in vitro and in vivo studies

BACKGROUND

Antimicrobial photodynamic therapy uses photosensitizers designed to bind to microorganisms and generate reactive oxygen species when illuminated with visible light.

MATERIALS & METHODS

We synthesized a highly water-soluble [70]fullerene monoadduct, C70[>M(C3N6(+)C3)2]-(I(-))10 (LC17), and bisadduct, C70[>M(C3N6(+)C3)2][>M(C3N6C3)2] (LC18), both with a well-defined decacationic quaternary ammonium iodide moiety with ten positive charges per C70 to give water solubility and bacterial binding. We determined the antimicrobial effects against human pathogens, Gram-positive (Staphylococcus aureus) and Gram-negative species (Escherichia coli and Acinetobacter baumannii) when activated by UVA or white light.

RESULTS

White light was more effective with LC17, while UVA light was more effective with LC18. Both compounds were effective in a mouse model of Gram-negative third-degree burn infections determined by bioluminescence imaging.

DISCUSSION & CONCLUSION

We propose that the attachment of an additional deca(tertiary-ethylenylamino)malonate arm to C70 allowed the moiety to act as a potent electron donor and increased the generation yield of hydroxyl radicals under UVA illumination.

Singlet oxygen in antimicrobial photodynamic therapy: photosensitizer-dependent production and decay in E. coli

Several families of photosensitizers are currently being scrutinized for antimicrobial photodynamic therapy applications. Differences in physical and photochemical properties can lead to different localization patterns as well as differences in singlet oxygen production and decay when the photosensitizers are taken up by bacterial cells. We have examined the production and fate of singlet oxygen in Escherichia coli upon photosensitization with three structurally-different cationic photosensitizers, namely New Methylene Blue N (NMB), a member of the phenothiazine family, ACS268, a hydrophobic porphyrin with a single cationic alkyl chain, and zinc(II)-tetramethyltetrapyridinoporphyrazinium salt, a phthalocyanine-like photosensitizer with four positive charges on the macrocycle core. The kinetics of singlet oxygen production and decay indicate different localization for the three photosensitizers, whereby NMB appears to localize in an aqueous-like microenvironment, whereas ACS268 localizes in an oxygen-shielded site, highly reactive towards singlet oxygen. The tetracationic zinc(II) tetrapyridinoporphyrazine is extensively aggregated in the bacteria and fails to produce any detectable singlet oxygen.

Emerging therapies for multidrug resistant Acinetobacter baumannii

The global emergence of multidrug resistant Acinetobacter baumannii has reduced the number of clinically available antibiotics that retain activity against this pathogen. For this reason, the development of novel prevention and treatment strategies for infections caused by A. baumannii is necessary. Several studies have begun to characterize nonantibiotic approaches that utilize novel mechanisms of action to achieve antibacterial activity. Recent advances in phage therapy, iron chelation therapy, antimicrobial peptides, prophylactic vaccination, photodynamic therapy, and nitric oxide (NO)-based therapies have all been shown to have activity against A. baumannii. However, before these approaches can be used clinically there are still limitations and remaining questions that must be addressed.

Chitosan nanoparticles for antimicrobial photodynamic inactivation: characterization and in vitro investigation

The growing resistance to antibiotics has rendered antimicrobial photodynamic inactivation (PDI) an attractive alternative treatment modality for infectious diseases. Chitosan (CS) was shown to further potentiate the PDI effect of photosensitizers and was therefore used in this study to investigate its ability to potentiate the activity of erythrosine (ER) against bacteria and yeast. CS nanoparticles loaded with ER were prepared by ionic gelation method and tested for their PDI efficacy on planktonic cells and biofilms of Streptococcus mutans, Pseudomonas aeruginosa and Candida albicans. The nanoparticles were characterized for their size, polydispersity index and zeta potential. No toxicity was observed when planktonic cells and biofilms were treated with the nanoparticles in the dark. However, when the cells were exposed to light irradiation after treatment with free ER or ER/CS nanoparticles, a significant phototoxicity was observed. The antimicrobial activity of ER/CS nanoparticles was significantly higher than ER in free form. The particle size and incubation time of the nanoparticles also appeared to be important factors affecting their PDI activity against S. mutans and C. albicans.

In vitrophotosensitizing efficacy of cationic phthalocyanine derivatives againstC.albicans: effect of serum albumins

The effect of serum albumins (as Fetal Calf Serum) on in vitro photosensing efficacy against C.albicans of three cationic Zn ( II ) phthalocyanine derivatives was evaluated. A clearly structure-dependent reduction in the antifungine activity was observed. For this reason the binding of the photosensitizers with albumins (as bovine serum albumin, BSA) at pH 7.4 was studied. Because of aggregation phenomena, the phthalocyanine derivatives showed little fluorescence in aqueous solutions and fluorescence intensity increased as a function of protein concentration. Titration plots were built and binding constant were determined. The obtained binding parameters and the hydrolipophilic properties of the studied molecules (octanol/water partition coefficient PO / W, number of cationic charges, amphipilicity) were correlated with the observed biological effect.

Synthesis of asymmetricallymeso-substituted porphyrins bearing amino groups as potential cationic photodynamic agents

Novel asymmetrically meso-substituted porphyrins bearing amino groups have been synthesized as precursors of cationic photodynamic agents. The amphiphilic character of these porphyrins was increased by the presence of a high lipophilic trifluoromethyl group. Different patterns of porphyrin structures were obtained from meso-4-[(3- N , N -dimethylaminopropoxy)phenyl] dipyrromethane 1, which was formed by the condensation of 4-(3- N , N -dimethylaminopropoxy) benzaldehyde with a large excess of pyrrole. This reaction takes place at high temperature with a yield of 59%. This reaction was also attempted under acid-catalyzed condensation at room temperature. However, under these conditions, the amino group reduces the catalyst and the reaction does not take place. To obtain porphyrins, dipyrromethane 1 was condensed with aldehydes in the presence of trifluoroacetic acid ( TFA ) under different conditions. First, 1 reacted with 4-(3- N , N -dimethylaminopropoxy)benzaldehyde in dichloromethane catalyzed by TFA (∼4 times TFA /1 molar ratio) to obtain 6.2% of 5,10,15,20-tetrakis(4-[3- N , N -dimethylaminopropoxy]phenyl)porphyrin ( A4-porphyrin). Under similar conditions, reaction of 1 with 4-(trifluoromethyl)benzaldehyde produces 5,15-di(4-[3- N , N -dimethylaminopropoxy]phenyl)-10,20-di(4-trifluoromethylphenyl)porphyrin ( A2B2- porphyrin ) with a 4.8% yield. This procedure also yields a mixture of porphyrins, which were formed due to acidolysis of 1. When a minor amount of TFA was used in acetonitrile, the yield of A2B2-porphyrin was very poor (∼0.4%). On the other hand, condensation of 1 with 4-trifluoromethylbenzaldehyde and 4-(3- N , N -dimethylaminopropoxy)benzaldehyde catalyzed by TFA (∼2 times TFA /1 molar ratio) in acetonitrile yields 9.3% of 5-(4-trifluoromethylphenyl)-10,15,20-tris(4-[3- N , N -dimethylaminopropoxy]phenyl)porphyrin ( A3B-porphyrin ). A2B2and A4porphyrins were also isolated with 6.0 and 2.0%, respectively. Finally, exhaustive methylation of amino porphyrins produces cationic sensitizers (>94% yield). Absorption and fluorescence spectroscopic studies of these sensitizers were compared in N , N -dimethylformamide. In these porphyrins, the cationic centers are isolated from the porphyrin ring by a propoxy bridge. Thus, the cationic charges have minimal influence on the photophysical properties of the sensitizers. In addition, this chain provides a higher mobility of the charge, which could facilitate interaction with the outer membrane of the Gram-negative bacteria. These amphiphilic cationic porphyrins are promising photosensitizers with potential applications in bacterial inactivation by photodynamic therapy.

Mechanistic aspects of photoinactivation of Candida albicans by exogenous porphyrins

The mechanism of photoinactivation of Candida albicans by 3.5 μM uncharged, cationic or anionic porphyrins under blue light (407-420 nm) was found to be dependent on the uptake of porphyrins into yeast cells, and was also dependent on the presence or absence of proteins in the photosensitization medium. In a very protein-rich medium, a decrease in viability was observed only with the uncharged porphyrin. Photoinactivation by uncharged or cationic porphyrins in a protein-poorer medium resulted in total eradication, whereas no significant decrease was observed with the anionic porphyrin. Phototreatment in PBS resulted in eradication with all three porphyrins. X-ray microanalysis after phototreatment by the uncharged or cationic porphyrins in the protein-poor medium exhibited ion loss, indicating cell-membrane damage. Transmission electron microscopy indicated cellular and chromosomal damage. No ion loss or cell damage was observed in this medium with the anionic porphyrin. The efficiency of photoeradication of C. albicans is dependent on porphyrin uptake, which might lead (upon illumination) to processes that facilitate the formation of reactive oxygen species that damage the cells. Uptake of charged porphyrins is dependent on protein quantity and quality in the photosensitization microenvironment. This fact must be taken into account when using charged photosensitizers.

Extracellular heme uptake and the challenges of bacterial cell membranes

In bacteria, the fine balance of maintaining adequate iron levels while preventing the deleterious effects of excess iron has led to the evolution of sophisticated cellular mechanisms to obtain, store, and regulate iron. Iron uptake provides a significant challenge given its limited bioavailability and need to be transported across the bacterial cell wall and membranes. Pathogenic bacteria have circumvented the iron-availability issue by utilizing the hosts' heme-containing proteins as a source of iron. Once internalized, iron is liberated from the porphyrin enzymatically for cellular processes within the bacterial cell. Heme, a lipophilic and toxic molecule, poses a significant challenge in terms of transport given its chemical reactivity. As such, pathogenic bacteria have evolved sophisticated membrane transporters to coordinate, sequester, and transport heme. Recent advances in the biochemical and structural characterization of the membrane-bound heme transport proteins are discussed in the context of ligand coordination, protein-protein interaction, and heme transfer.

Photodynamic inactivation of bacteria using polyethylenimine-chlorin(e6) conjugates: Effect of polymer molecular weight, substitution ratio of chlorin(e6) and pH

BACKGROUND AND OBJECTIVES

Antimicrobial photodynamic therapy (APDT) is a novel technique to treat local infections. Previously we reported that the attachment of chlorin(e6) to polyethylenimine (PEI) polymers to form PEI-ce6 conjugates is an effective way to improve ce6 PDT activity against bacteria. The aim of this work was to explore how the polymer molecular weight, substitution ratio (SR) of ce6 and pH value affect the PDT efficacy.

STUDY DESIGN/MATERIALS AND METHODS

We have synthesized PEI-ce6(10) (MW = 60,000, SR = 1) and PEI-ce6(11) (MW = 60,000, SR = 5) and compared these with the previous PEI-ce6(9) (MW = 10,000, SR = 1). We tested the PDT efficacy of these three conjugates against Gram-negative E. coli and Gram-positive bacteria (S. aureus and E. fecalis) at three different pH values (5.0, 7.4, 10.0) that may affect the charge on both the bacterial cells and on the conjugate (that has both basic and acidic groups).

RESULTS

PEI-ce6(9) and PEI-ce6(10) were the most effective against these tested bacteria. The PDT effect of all three conjugates depended on pH values. The effective order was pH = 10.0 > pH = 7.4 > pH = 5.0 on E. coli. For S. aureus and E. fecalis the order was pH = 5.0 > pH = 10.0 > pH = 7.4. PEI-ce6(11) PDT activity was worse than PEI-ce6(10) activity which is probably connected to the fact that ce6 molecules are self-quenched within the PEI-ce6(11) molecule. Ce6 quenching within the PEI-ce6 molecules was proved by analyzing fluorescence spectra of PEI-ce6 conjugates at different pH values. There were no differences in bacterial uptake between different pH values in three PEI-ce6 conjugates.

CONCLUSION

We assume high pH (rather than low pH as was hypothesized) disaggregates the conjugates, so the higher pH was more effective than the lower pH against E. coli. But for Gram-positive bacteria, low pH was more effective possibly due to more overall positive charge on the conjugate.

Photodynamic antimicrobial chemotherapy by liposome-encapsulated water-soluble photosensitizers

Photodynamic antimicrobial chemotherapy is an alternative method for killing bacterial cells in view of the increasing problem of multi-antibiotic resistance. We examined the effect of three water-soluble photosensitizers (PhS): methylene blue (MB), neutral red (NR) and rose bengal (RB) on Gram-positive and Gram-negative bacteria. We compared the efficacy of PhS in their free form and encapsulated in liposomal formulations against various bacterial strains, and determined conditions for the effective use of encapsulated PhS. We found that all three PhS were able to eradicate the Gram-positive microbes Staphylococcus aureus and Sarcina lutea; and MB and RB were effective against St. epidermidis. In the case of the Gram-negative species, MB and RB were cytotoxic against the Shigella flexneri, NR-inactivated Escherichia coli and Salmonella para B, and BR was effective in killing Pseudomonas aeruginosa. None of the examined PhS showed activity against Klebsiella pneumoniae. MB and NR enclosed in liposomes gave a stronger antimicrobial effect than free PhS for all tested prokaryotes, whereas encapsulation of RB led to no increase in its activity. We suggest that encapsulation of PhS can increase the photoinactivation of bacteria.

Photodynamic therapy for localized infections--state of the art

Photodynamic therapy (PDT) was discovered over 100 years ago by observing the killing of microorganisms when harmless dyes and visible light were combined in vitro. Since then it has primarily been developed as a treatment for cancer, ophthalmologic disorders and in dermatology. However, in recent years interest in the antimicrobial effects of PDT has revived and it has been proposed as a therapy for a large variety of localized infections. This revival of interest has largely been driven by the inexorable increase in drug resistance among many classes of pathogen. Advantages of PDT include equal killing effectiveness regardless of antibiotic resistance, and a lack of induction of PDT resistance. Disadvantages include the cessation of the antimicrobial effect when the light is turned off, and less than perfect selectivity for microbial cells over host tissue. This review will cover the use of PDT to kill or inactivate pathogens in ex vivo tissues and in biological materials such as blood. PDT has been successfully used to kill pathogens and even to save life in several animal models of localized infections such as surface wounds, burns, oral sites, abscesses and the middle ear. A large number of clinical studies of PDT for viral papillomatosis lesions and for acne refer to its antimicrobial effect, but it is unclear how important this microbial killing is to the overall therapeutic outcome. PDT for periodontitis is a rapidly growing clinical application and other dental applications are under investigation. PDT is being clinically studied for other dermatological infections such as leishmaniasis and mycobacteria. Antimicrobial PDT will become more important in the future as antibiotic resistance is only expected to continue to increase.

Decorating parylene-coated glass with ZnO nanoparticles for antibacterial applications: a comparative study of sonochemical, microwave, and microwave-plasma coating routes

A glass substrate, coated with a Parylene film, was coated with ZnO by three different methods: ultrasound, microwave, and microwave-plasma irradiation. These coating modes are simple, efficient, and environmentally friendly one-step processes. The structure of the coated products was characterized and compared using methods such as XRD, HR-SEM, EDS, RBS, and optical spectroscopy. Coating by ZnO nanoparticles was achieved for all three approaches. The products were found to differ in their particle sizes, coating thickness, and depth of penetration. All of the ZnO-Parylene-glass composites demonstrated a significant antibacterial activity against Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive) strains.

Photodynamic inactivation of Escherichia coli and Streptococcus mitis by cationic zinc(II) phthalocyanines in media with blood derivatives

The photodynamic inactivation (PDI) of Escherichia coli and Streptococcus mitis sensitized by cationic phthalocyanines was studied in different media containing blood derivatives. First, the activity of zinc(II) tetramethyltetrapyridino[3,4-b:3',4'-g:3'',4''-l:3''',4'''-q]porphyrazinium (ZnAPc4+), zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine (ZnPPc4+) and zinc(II) 2,9,16,23-tetrakis[2-(N,N,N-trimethylamino)ethoxy]phthalocyanine (ZnEPc4+) were compared to photoinactivate these bacteria in saline solutions. After visible light irradiation, a higher photoinactivation of E. coli cells was found for ZnPPc4+, while ZnEPc4+ was the more effective sensitizer to eradicate S. mitis cells. In the presence of human red blood (HRB) cells, two aspects were analyzed: the photohemolysis induced by these cationic phthalocyanines and the PDI of bacteria in medium containing erythrocytes. The highest photohemolytic damage was produced by ZnPPc4+, which can be avoided using azida ion as photoprotective quencher. In both bacteria, the photoinactivation is possible in presence of HRB cells. Mainly, ZnEPc4+ is effective to photoinactivate S. mitis with a low hemolysis of erythrocytes. However, inactivation of E. coli by ZnPPc4+ decreases in medium with HRB cells, further when azide ion is added to avoid hemolysis. The presence of plasma considerable reduces the photocytotoxic effect, which mainly affects the eradication of E. coli. However, the PDI of S. mitis by ZnEPc4+ is even possible in presence of blood derivatives.

Photosensitizer-antibiotic conjugates: a novel class of antibacterial molecules

Bacterial resistance to a variety of antibiotics has led to intensive research into the effect of photosensitizers as a cytotoxic agent against bacterial cells. In this study, we synthesized the following conjugates with or without a linker: rose bengal-penicillanic acid (RBPA), rose bengal-linker-penicillanic acid (RBLPA) and rose bengal-linker-kanamycin (RBLKAN). The antibacterial activity of these conjugates was examined on Staphylococcus aureus and Escherichia coli. Exposure of the cultures to 100 J cm(-2) showed that the minimum inhibitory concentration (MIC) of RBPA, RBLPA and RBLKAN on S. aureus was 0.195, 0.156 and 0.004 microm, respectively. The MIC of RBPA, RBLPA and RBLKAN on E. coli was 1.56, 2.5 and 0.156 microm, respectively. In dark control experiments, the MIC of these conjugates was not detected until a concentration that was 16-fold that of the MIC found in the light experiments. RBPA and RBLPA as well as RBLKAN are bactericidal for both bacterial cells. Total eradication of S. aureus and E. coli was observed with RBLKAN (0.078 and 20 microm 16 J cm(-2), respectively). Under these conditions, scanning electron microscopic analysis showed significant damage to these bacteria. However, the photosensitizer and antibiotics individually were not effective.

Phage therapy and photodynamic therapy: low environmental impact approaches to inactivate microorganisms in fish farming plants

Owing to the increasing importance of aquaculture to compensate for the progressive worldwide reduction of natural fish and to the fact that several fish farming plants often suffer from heavy financial losses due to the development of infections caused by microbial pathogens, including multidrug resistant bacteria, more environmentally-friendly strategies to control fish infections are urgently needed to make the aquaculture industry more sustainable. The aim of this review is to briefly present the typical fish farming diseases and their threats and discuss the present state of chemotherapy to inactivate microorganisms in fish farming plants as well as to examine the new environmentally friendly approaches to control fish infection namely phage therapy and photodynamic antimicrobial therapy.

Delivery of Methylene Blue and meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate from cross-linked poly(vinyl alcohol) hydrogels: a potential means of photodynamic therapy of infected wounds

Poly(vinyl alcohol)-borate complexes were evaluated as a potentially novel drug delivery platform suitable for in vivo use in photodynamic antimicrobial chemotherapy (PACT) of wound infections. An optimised formulation (8.0%w/w PVA, 2.0%w/w borax) was loaded with 1.0 mg ml(-1) of the photosensitisers Methylene Blue (MB) and meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate (TMP). Both drugs were released to yield receiver compartment concentrations (>5.0 microg ml(-1)) found to be phototoxic to both planktonic and biofilm-grown methicillin-resistant Staphylococcus aureus (MRSA), a common cause of wound infections in hospitals. Newborn calf serum, used to simulate the conditions prevalent in an exuding wound, did not adversely affect the properties of the hydrogels and had no significant effect on the rate of TMP-mediated photodynamic kill of MRSA, despite appreciably reducing the fluence rate of incident light. However, MB-mediated photodynamic kill of MRSA was significantly reduced in the presence of calf serum and when the clinical isolate was grown in a biofilm. Results support the contention that delivery of MB or TMP using gel-type vehicles as part of PACT could make a contribution to the photodynamic eradication of MRSA from infected wounds.

A potential antimicrobial treatment against ESBL-producing Klebsiella pneumoniae using the tellurium compound AS101

Due to the extensive spread of antibiotic-resistant Klebsiella pneumoniae, the non-toxic immunomodulator, ammonium trichloro (dioxoethylene-o, o') tellurate (AS101), was introduced for the first time in this study. Eleven strains of K. pneumoniae were tested: five were extended spectrum beta lactamase (ESBL)-producing strains and six were non-ESBL-producing strains. The MIC and MBC of ten strains were 9 microg/ml AS101 and 18 microg/ml for one strain. AS101 treatment inhibited bacterial growth in a dose-dependent manner on protein-rich media. No inhibition by AS101 was observed on poorer media. In combination with beta-mercaptoethanol (2-ME) or cysteamine, AS101 inhibited bacterial growth in both types of media. Growth inhibition was also shown following AS101 treatment at both lag and log phases. Our data indicate that AS101 enters the bacterium through its porins, causing bacterial destruction. The mechanism of cell death was characterized using several techniques: (a) scanning electron microscopy showed that bacteria treated with AS101 or in combination with cysteamine exhibited evidence of cell-wall damage; (b) X-ray microanalysis demonstrated damage to Na/K pumps; and (c) transmission electron microscopy demonstrated cell lysis. These phenomena suggest that AS101 has antibacterial potential against K. pneumoniae infections.

Charge effect on the photoinactivation of Gram-negative and Gram-positive bacteria by cationic meso-substituted porphyrins

BACKGROUND

In recent times photodynamic antimicrobial therapy has been used to efficiently destroy Gram (+) and Gram (-) bacteria using cationic porphyrins as photosensitizers. There is an increasing interest in this approach, namely in the search of photosensitizers with adequate structural features for an efficient photoinactivation process. In this study we propose to compare the efficiency of seven cationic porphyrins differing in meso-substituent groups, charge number and charge distribution, on the photodynamic inactivation of a Gram (+) bacterium (Enterococcus faecalis) and of a Gram (-) bacterium (Escherichia coli). The present study complements our previous work on the search for photosensitizers that might be considered good candidates for the photoinactivation of a large spectrum of environmental microorganisms.

RESULTS

Bacterial suspension (10(7) CFU mL(-1)) treated with different photosensitizers concentrations (0.5, 1.0 and 5.0 microM) were exposed to white light (40 W m(-2)) for a total light dose of 64.8 J cm(-2). The most effective photosensitizers against both bacterial strains were the Tri-Py+-Me-PF and Tri-Py+-Me-CO2Me at 5.0 microM with a light fluence of 64.8 J cm(-2), leading to > 7.0 log (> 99,999%) of photoinactivation. The tetracationic porphyrin also proved to be a good photosensitizer against both bacterial strains. Both di-cationic and the monocationic porphyrins were the least effective ones.

CONCLUSION

The number of positive charges, the charge distribution in the porphyrins' structure and the meso-substituent groups seem to have different effects on the photoinactivation of both bacteria. As the Tri-Py+-Me-PF porphyrin provides the highest log reduction using lower light doses, this photosensitizer can efficiently photoinactivate a large spectrum of environmental bacteria. The complete inactivation of both bacterial strains with low light fluence (40 W m(-2)) means that the photodynamic approach can be applied to wastewater treatment under natural light conditions which makes this technology cheap and feasible in terms of the light source.

A possible mechanism for visible light-induced wound healing

BACKGROUND AND OBJECTIVES

Chronic wounds resistant to conventional therapy have been treated successfully with low energy lasers and light emitting diodes (LEDs) in the visible and near IR region. It has been proposed that production of low level reactive oxygen species (ROS) following illumination is the first step of photobiomodulation. It was also shown that white light (400-800 nm) has similar stimulatory effects as lasers and LEDs. ROS at higher levels are toxic to cells and bacteria.

STUDY DESIGN/MATERIALS AND METHODS

In the present study, we examined the phototoxicity of broadband (400-800 nm, 120 J/cm(2)) visible light on the survival of several pathogenic bacteria: Staphylococcus aureus 195, Pseudomonas aeruginosa 1316, Escherichia coli 1313, and Serratia marcescens. These bacteria were chosen due to their high prevalence in infected wounds. The survival of bacterial cells following illumination was monitored by counting the number of colony forming units before and after exposure to light.

RESULTS

Illumination with white light, 120 J/cm(2), caused a reduction of 62%, 83%, and 56% in the colony count of E. coli 1313, S. aureus 195 and S. marcescens, respectively, though no reduction in the viability of P. aeruginosa 1316 was demonstrated. The phototoxic effect was found to involve induction of ROS production by the bacteria. It was also found that illumination of S. aureus 195 and E. coli 1313 in the presence of pyocyanin, known to be secreted by P. aeruginosa, had a stronger bactericidal effect compared to illumination alone.

CONCLUSION

Visible light at high intensity can kill bacteria in infected wounds. Thus, illumination of infected wounds with intense visible light, prior to low intensity illumination for stimulating wound closure, may reduce infection and promote healing.

Tandem dispersion and killing of bacteria from a biofilm

The combined effects of biofilm dispersion with a 2-aminoimidazole-triazole conjugate and bactericidal activity with a photodynamic inactivation agent suggest a novel combination therapy for treating diverse microbial infections.

Depositing silver nanoparticles on/in a glass slide by the sonochemical method

A glass substrate was coated with silver by ultrasound irradiation. The structure and morphology of the nanoparticles in the deposited film were characterized using methods such as XRD, TEM, HR TEM, HRSEM, AFM, TOF-SIMS and optical spectroscopy. It was demonstrated that nucleation and the ensuing growth of the nanoparticles occurs in solution and is influenced by the concentration of the precursor, temperature and time of sonication. TOF-SIMS measurements revealed that silver nanoparticles passed through the glass interface and diffused within the glass substrate up to ∼60 nm. An analysis of the thermal effects accompanying the sonochemical cavitation of micro-bubbles in the solution near the solid surfaces shows that the collision of nanoparticles can lead to their melting and coalescence. Sonochemical deposition takes place layer by layer, so that the completion of the deposition of each layer of nanoparticles is followed by the sintering of adjacent particles and the formation of a close-packed layer. Using PVP as a stabilizing agent, a monolayer coating of silver nanoparticles on the glass surface was obtained. The coated glass demonstrated antibacterial activity.