Efflux pump inhibitor potentiates antimicrobial photodynamic inactivation of Enterococcus faecalis biofilm

Antimicrobial photodynamic therapy using Indocyanine green and near-infrared diode laser in reducing Entrerococcus faecalis

BACKGROUND

The use of Antimicrobial Photodynamic Therapy (aPDT) has been suggested as an adjuvant method to eliminate facultative bacteria during root canal disinfection. The purpose of this preliminary in vitro study was to determine whether the light-activated antimicrobial agent, Indocyanine green (ICG), could be used as photosensitizer and kill Enterococcus faecalis strain under planktonic conditions when irradiated with near-infared (NIR) diode laser emitting in 810nm wavelength.

METHODS

Planktonic suspension containing Enterococcus faecalis strain was divided into nine experimental groups: (1) aPDT with ICG and laser (medium energy fluence), (2) aPDT with ICG and laser (high energy fluence), (3) only ICG without laser activation, (4) only laser emission without ICG (5) 2.5% Sodium hypochlorite (NaOCl) as irrigant, (6) 2.5% NaOCl and aPDT with ICG and laser, (7) 2.0% Chlorhexidine gluconate (CHX) as irrigant (8) No treatment (positive control), (9) No bacterial biofilm growth (negative control). The samples were incubated for 7days and colony-forming units (CFUs) were determined to evaluate bacterial viability.

RESULTS

The microbiological test revealed that aPDT groups, regardless the overall power, showed significant lower mean log₁₀ CFU levels, than groups 3, 4 and 7 (p<0.01). The irrigation with 2.5% NaOCl and the combination of PDT and NaOCl achieved total elimination of bacteria.

CONCLUSION

These preliminary in vitro findings imply that the combination of ICG and NIR diode laser may be a novel supplement in aPDT and provide better disinfection during endodontic treatment.

Chitosan nanoparticles enhance the efficiency of methylene blue-mediated antimicrobial photodynamic inactivation of bacterial biofilms: An in vitro study

BACKGROUND

Biodegradable chitosan nanoparticles (CSNPs) with an intrinsic antimicrobial activity may be a good choice to improve the effectiveness of antimicrobial photodynamic inactivation (APDI). The aim of this study was to investigate the effect of CSNPs on the efficiency of methylene blue (MB)-mediated APDI of Staphylococcus aureus and Pseudomonas aeruginosa biofilms. We also assessed the phototoxicity of MB+CSNPs towards human fibroblasts.

METHODS

CSNPs were prepared using ionic gelation method and characterized by dynamic light scattering (DLS) and field-emission scanning electron microscope (FESEM). Biofilms were developed in a 96-well polystyrene plate for 24h. In vitro phototoxic effect of MB+CSNPs (at final concentrations of 50μM MB) at fluence of 22.93J/cm(2)) on biofilms were studied. Appropriate controls were included. Also, in vitro cytotoxicity and phototoxicity of the above mixture was assessed on human dermal fibroblasts.

RESULTS

DLS and FESEM measurements confirmed the nanometric size of the prepared CSNPs. APDI mediated by the mixture of MB and CSNPs showed significant anti-biofilm photoinactivation (P<0.001, >3 and >2 log10 CFU reduction in S. aureus and P. aeruginosa biofilms, respectively) while MB-induced APDI led to approximately <1 log10 CFU reduction. At the same experimental conditions, only 25.1% of the fibroblasts were photoinactivated by MB+CSNPs.

CONCLUSION

Our findings showed that CSNPs enhanced the efficacy of MB-APDI; it may be due to the disruption of biofilm structure by polycationic CSNPs and subsequently deeper and higher penetration of MB into the biofilms.

Effect of gaseous ozone on Enterococcus faecalis biofilm-an in vitro study

OBJECTIVES

The aim of this study was to evaluate the antimicrobial effect of gaseous ozone compared to conventional methods against Enterococcus faecalis.

MATERIALS AND METHODS

One hundred twenty-five teeth were infected by E. faecalis and were incubated for 72 h to form biofilm. Teeth were distributed among five groups. In the first group, ozone was used; in the second group, teeth were rinsed with 20 % ethylenediaminetetraacetic acid (EDTA); in the third group, with 3 % sodium hypochlorite (NaOCl). Group 4 combined 20 % EDTA with ozone. NaOCl and ozone were combined in group 5. After treatment, the samples with paper points were taken, followed by dentin samples taken with K-file, and cultured for 24 h. Then bacterial colonies were counted.

RESULTS

All treatments reduced significantly (p < 0.05) the bacteria. Paper points' samples showed 85.38 % reduction after ozone. The highest reduction was observed in NaOCl group (99.98 %). EDTA reduced bacteria by 80.64 %. Combination of NaOCl and ozone eradicated 99.95 % of the bacteria. Combination of EDTA and ozone reduced E. faecalis up to 91.33 %. The dentin chips showed the following: the highest CFU counts were observed in EDTA group, followed by ozone and NaOCl group. The lowest CFU counts were found in NaOCl-ozone group and EDTA-ozone group.

CONCLUSIONS

Ozone reduced E. faecalis, even organised in a biofilm, however, lower than NaOCl. No treatment reduced totally the bacteria.

CLINICAL RELEVANCE

Used as an adjuvant, ozone can increase the efficacy of conventional rinsing like EDTA and presents an alternative treatment when NaOCl cannot be used e.g. in teeth with a wide-open apical foramen.

Antibacterial photodynamic therapy: overview of a promising approach to fight antibiotic-resistant bacterial infections

Antibacterial photodynamic therapy (APDT) has drawn increasing attention from the scientific society for its potential to effectively kill multidrug-resistant pathogenic bacteria and for its low tendency to induce drug resistance that bacteria can rapidly develop against traditional antibiotic therapy. The review summarizes the mechanism of action of APDT, the photosensitizers, the barriers to PS localization, the targets, the in vitro-, in vivo-, and clinical evidence, the current developments in terms of treating Gram-positive and Gram-negative bacteria, the limitations, as well as future perspectives. Relevance for patients: A structured overview of all important aspects of APDT is provided in the context of resistant bacterial species. The information presented is relevant and accessible for scientists as well as clinicians, whose joint effort is required to ensure that this technology benefits patients in the post-antibiotic era.

Carboranyl-Chlorin e6 as a Potent Antimicrobial Photosensitizer

Antimicrobial photodynamic inactivation is currently being widely considered as alternative to antibiotic chemotherapy of infective diseases, attracting much attention to design of novel effective photosensitizers. Carboranyl-chlorin-e₆ (the conjugate of chlorin e₆ with carborane), applied here for the first time for antimicrobial photodynamic inactivation, appeared to be much stronger than chlorin e₆ against Gram-positive bacteria, such as Bacillus subtilis, Staphyllococcus aureus and Mycobacterium sp. Confocal fluorescence spectroscopy and membrane leakage experiments indicated that bacteria cell death upon photodynamic treatment with carboranyl-chlorin-e₆ is caused by loss of cell membrane integrity. The enhanced photobactericidal activity was attributed to the increased accumulation of the conjugate by bacterial cells, as evaluated both by centrifugation and fluorescence correlation spectroscopy. Gram-negative bacteria were rather resistant to antimicrobial photodynamic inactivation mediated by carboranyl-chlorin-e₆. Unlike chlorin e₆, the conjugate showed higher (compared to the wild-type strain) dark toxicity with Escherichia coli ΔtolC mutant, deficient in TolC-requiring multidrug efflux transporters.

The impact of absorbed photons on antimicrobial photodynamic efficacy

Due to increasing resistance of pathogens toward standard antimicrobial procedures, alternative approaches that are capable of inactivating pathogens are necessary in support of regular modalities. In this instance, the photodynamic inactivation of bacteria (PIB) may be a promising alternative. For clinical application of PIB it is essential to ensure appropriate comparison of given photosensitizer (PS)-light source systems, which is complicated by distinct absorption and emission characteristics of given PS and their corresponding light sources, respectively. Consequently, in the present study two strategies for adjustment of irradiation parameters were evaluated: (i) matching energy doses applied by respective light sources (common practice) and (ii) by development and application of a formula for adjusting the numbers of photons absorbed by PS upon irradiation by their corresponding light sources. Since according to the photodynamic principle one PS molecule is excited by the absorption of one photon, this formula allows comparison of photodynamic efficacy of distinct PS per excited molecule. In light of this, the antimicrobial photodynamic efficacy of recently developed PS SAPYR was compared to that of clinical standard PS Methylene Blue (MB) regarding inactivation of monospecies biofilms formed by Enterococcus faecalis and Actinomyces naeslundii whereby evaluating both adjustment strategies. PIB with SAPYR exhibited CFU-reductions of 5.1 log₁₀ and 6.5 log₁₀ against E. faecalis and A. naeslundii, respectively, which is declared as a disinfectant efficacy. In contrast, the effect of PIB with MB was smaller when the applied energy dose was adjusted compared to SAPYR (CFU-reductions of 3.4 log₁₀ and 4.2 log₁₀ against E. faecalis and A. naeslundii), or there was even no effect at all when the number of absorbed photons was adjusted compared to SAPYR. Since adjusting the numbers of absorbed photons is the more precise and adequate method from a photophysical point of view, this strategy should be considered in further studies when antimicrobial efficacy rates of distinct PS-light source systems are compared.

Fluid Dynamics and Biofilm Removal Generated by Syringe-delivered and 2 Ultrasonic-assisted Irrigation Methods: A Novel Experimental Approach

INTRODUCTION

Thorough understanding of fluid dynamics in root canal irrigation and corresponding antibiofilm capacity will support improved disinfection strategies. This study aimed to develop a standardized, simulated root canal model that allows real-time analysis of fluid/irrigation dynamics and its correlation with biofilm elimination.

METHODS

A maxillary incisor with an instrumented root canal was imaged with micro-computed tomography. The canal volume was reconstructed in 3 dimensions and replicated in soft lithography-based models microfabricated from polyethylene glycol-modified polydimethylsiloxane. Canals were irrigated by using a syringe (SI) and 2 ultrasonic-assisted methods, intermittent (IUAI) and continuous (CUAI). Real-time fluid movement within the apical 3 mm of canals was imaged by using microparticle image velocimetry. In similar models, canals were inoculated with Enterococcus faecalis to grow 3-week-old biofilms. Biofilm reduction by irrigation with SI, CUAI, and IUAI was assessed by using a crystal violet assay and compared with an untreated control.

RESULTS

SI generated higher velocity and shear stress in the apical 1-2 mm than 0-1 and 2-3 mm. IUAI generated consistently low shear stress in the apical 3 mm. CUAI generated consistently high levels of velocity and shear stress; it was the highest of the groups in the apical 0-1 and 2-3 mm. Biofilm was significantly reduced compared with the control only by CUAI (two-sample permutation test, P = .005).

CONCLUSIONS

CUAI exhibited the highest mechanical effects of fluid flow in the apical 3 mm, which correlated with significant biofilm reduction. The soft lithography-based models provided a novel model/method for study of correlations between fluid dynamics and the antibiofilm capacity of root canal irrigation methods.

Antimicrobial photodynamic activity of hypericin against methicillin-susceptible and resistant Staphylococcus aureus biofilms

ABSTRACT 

Aim: To evaluate the effectiveness of the photodynamic therapy using hypericin (HYP) against both planktonic and biofilm-forming Staphylococcus aureus. Materials & methods: HYP photoactivity was evaluated against methicillin-susceptible and resistant S. aureus. Bacterial suspension or biofilm were preincubated with HYP and subjected to LED illumination. Viable bacteria were determined by colony counting. Results: Preincubation with HYP (5 min) plus light exposure (10 min) showed bactericidal effect against planktonic methicillin-susceptible S. aureus and methicillin-resistant S. aureus. Longer preincubation times (24 h) and time light exposure (30 min) were required to reach HYP-photoactivity against S. aureus biofilms. HYP-photoactivity was correlated to the biofilm production. Conclusion: HYP could be a potential photosensitizer for the inactivation of staphylococcal biofilms forming on the surfaces accessible to visible light.

Photodynamic therapy: An adjunct to conventional root canal disinfection strategies

Although chemical-based root canal disinfectants are important to reduce microbial loads and remove infected smear layer from root dentin, they have only a limited ability to eliminate biofilm bacteria, especially from root complexities. This paper explores the novel photodynamic therapy (PDT) for antimicrobial disinfection of root canals. The combination of an effective photosensitizer, the appropriate wavelength of light and ambient oxygen is the key factor in PDT. PDT uses a specific wavelength of light to activate a non-toxic dye (photosensitizer), leading to the formation of reactive oxygen species. These reactive oxygen molecules can damage bacterial proteins, membrane lipids and nucleic acids, which promote bacterial cell death. In, addition PDT may enhance cross-linking of collagen fibrils in the dentin matrix and thereby improving dentin stability. The concept of PDT is plausible and could foster new therapy concepts for endodontics. The available knowledge should enable and encourage steps forward into more clinical-oriented research and development. This article discusses PDT as related to root canal disinfection, including its components, mechanism of action, reviews the current endodontic literature and also highlights the shortcomings and advancements in PDT techniques.

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.

Photodynamic therapy in combating the causative microorganisms from endodontic infections

Photodynamic therapy (PDT) is presented as a promising antimicrobial therapy that can eliminate microorganisms present in endodontic infections. This treatment is based on the use of a nontoxic photosensitizing agent followed by irradiation of a resonant light source being capable of generating highly reactive species that are harmful to microorganisms. The purpose of this paper is to review the dental literature about the main factors that encompass the use of PDT combined with endodontic treatment for decontamination of the root canal system. A literature search was performed using the following index databases: PubMed, ISI Web of Knowledge and MedLine, between 2000 and 2014, looking for studies regarding antimicrobial action of PDT and its application to endodontic therapy. It was observed that despite numerous promising results, it is still necessary to establish different parameters so that PDT can be used with maximum effectiveness in eliminating microorganisms that cause endodontic infections.

Antimicrobial photodynamic therapy for inactivation of biofilms formed by oral key pathogens

With increasing numbers of antibiotic-resistant pathogens all over the world there is a pressing need for strategies that are capable of inactivating biofilm-state pathogens with less potential of developing resistances in pathogens. Antimicrobial strategies of that kind are especially needed in dentistry in order to avoid the usage of antibiotics for treatment of periodontal, endodontic or mucosal topical infections caused by bacterial or yeast biofilms. One possible option could be the antimicrobial photodynamic therapy (aPDT), whereby the lethal effect of aPDT is based on the principle that visible light activates a photosensitizer (PS), leading to the formation of reactive oxygen species, e.g., singlet oxygen, which induce phototoxicity immediately during illumination. Many compounds have been described as potential PS for aPDT against bacterial and yeast biofilms so far, but conflicting results have been reported. Therefore, the aim of the present review is to outline the actual state of the art regarding the potential of aPDT for inactivation of biofilms formed in vitro with a main focus on those formed by oral key pathogens and structured regarding the distinct types of PS.

Comparative antibacterial efficacy of photodynamic therapy and ultrasonic irrigation against Enterococcus faecalis in vitro

Enterococcus faecalis poses a challenge to the efficacy of traditional root canal disinfection methods. This study was aimed to establish a synergistic root canal disinfection strategy combining ultrasonic irrigation with photodynamic therapy (PDT) together and to test its antibacterial efficacy against E. faecalis. Twenty-seven bovine root canals infected with E. faecalis were randomly divided into three groups and treated with different disinfection methods as follows: ultrasonic irrigation with 2.5% NaOCl, methylene blue (MB)-mediated PDT, or combined ultrasonic irrigation and PDT as described above. Quantification of E. faecalis was performed on the root canals before and immediately after the disinfection treatment. Residual bacteria were determined by counting colony-forming units. Samples were randomly selected from the three groups, and the morphology of residual bacteria inside the dentinal tubules was studied by scanning electron microscopy. The number of surviving E. faecalis in the group treated with the combination method was significantly lower (P < 0.05) than those in the ultrasonic irrigation-treated or PDT-treated groups. Similar results were found in the morphological studies of the three groups. The results of our study highlighted the importance of combination of ultrasonic irrigation and PDT to produce significant antibacterial efficacy against E. faecalis during root canal disinfection.

Antibiofilm efficacy of photosensitizer-functionalized bioactive nanoparticles on multispecies biofilm

INTRODUCTION

Newer disinfection strategies based on antibacterial nanoparticles and photodynamic therapy (PDT) aim to eliminate residual biofilm bacteria during root canal treatment. The aim of the current study was to test the newly developed rose bengal-functionalized chitosan nanoparticles (CSRBnps) for their interaction/uptake with monospecies bacteria/biofilm and assess their antibiofilm efficacy on a multispecies biofilm model in vitro.

METHODS

The interaction of CSRBnps with bacterial cells was conducted using atomic force microscopy. Their membrane-damaging effect was determined by measuring the absorbance at 260 nm (OD260nm) using Enterococcus faecalis. The penetration of CSRBnps into E. faecalis biofilms was evaluated using confocal laser scanning microscopy (CLSM). Multispecies biofilms of Streptococcus oralis, Prevotella intermedia, and Actinomyces naeslundii were grown on dentin sections for 21 days to assess the antibiofilm efficacy. The biofilms were subjected to PDT (60 J/cm(2)) using CSRBnps and rose bengal. The treated/untreated biofilms were examined under scanning electron microscopy and CLSM.

RESULTS

The CSRBnps synthesized were 60 ± 20 nm and showed absorption spectra similar to rose bengal. Atomic force microscopy showed adherence of CSRBnps to bacteria, roughening of cell surface, and cell disruption after PDT. CSRBnp treatment resulted in significantly increased bacterial membrane damage (P < .05). CSRBnps exhibited deeper penetration into the biofilm structure. Scanning electron microscopy and CLSM confirmed the complete disruption of multispecies biofilm with a reduction in viable bacteria and biofilm thickness (P < .05).

CONCLUSIONS

These novel photosensitizer functionalized bioactive nanoparticles with increased affinity to bacterial cell membrane, higher penetration into biofilm structure, and enhanced ability to eliminate clinically relevant multispecies bacterial biofilm present a potential antibiofilm agent for root canal disinfection.

Structural elucidation of SrtA enzyme in Enterococcus faecalis: an emphasis on screening of potential inhibitors against the biofilm formation

Enterococcus faecalis is a pathogenic Gram-positive bacterium, which mainly infects humans through urinary tract infections. SrtA is an essential enzyme for survival of E. faecalis, and inhibition of this particular enzyme will reduce the virulence of biofilm formation. It is proved to be associated with the microbial surface protein embedded signal transduction mechanism and promising as a suitable anti-microbial drug target for E. faecalis. The present work gives an inclusive description of SrtA isolated from E. faecalis through computational and experimental methodologies. For exploring the mechanism of SrtA and to screen potential leads against E. faecalis, we have generated three-dimensional models through homology modeling. The 3D model showed conformational stability over time, confirming the quality of the starting 3D model. Large scale 100 ns molecular dynamics simulations show the intramolecular changes occurring in SrtA, and multiple conformations of structure based screening elucidate potential leads against this pathogen. Experimental results showed that the screened compounds are active showing anti-microbial and anti-biofilm activity, as SrtA is known to play an important role in E. faecalis biofilm formation. Experimental results also suggest that SrtA specific screened compounds have better anti-biofilm activity than the available inhibitors. Therefore, we believe that development of these compounds would be an impetus to design the novel chief SrtA inhibitors against E. faecalis.

Photodynamic biofilm inactivation by SAPYR--an exclusive singlet oxygen photosensitizer

Prevention and control of biofilm-growing microorganisms are serious problems in public health due to increasing resistances of some pathogens against antimicrobial drugs and the potential of these microorganisms to cause severe infections in patients. Therefore, alternative approaches that are capable of killing pathogens are needed to supplement standard treatment modalities. One alternative is the photodynamic inactivation of bacteria (PIB). The lethal effect of PIB is based on the principle that visible light activates a photosensitizer, leading to the formation of reactive oxygen species, e.g., singlet oxygen, which induces phototoxicity immediately during illumination. SAPYR is a new generation of photosensitizers. Based on a 7-perinaphthenone structure, it shows a singlet oxygen quantum yield ΦΔ of 99% and is water soluble and photostable. Moreover, it contains a positive charge for good adherence to cell walls of pathogens. In this study, the PIB properties of SAPYR were investigated against monospecies and polyspecies biofilms formed in vitro by oral key pathogens. SAPYR showed a dual mechanism of action against biofilms: (I) it disrupts the structure of the biofilm even without illumination; (II) when irradiated, it inactivates bacteria in a polymicrobial biofilm after one single treatment with an efficacy of ≥ 99.99%. These results encourage further investigation on the potential of PIB using SAPYR for the treatment of localized infectious diseases.

Synergistic effect of microbubble emulsion and sonic or ultrasonic agitation on endodontic biofilm in vitro

INTRODUCTION

Irrigation dynamics and antibacterial activity determine the efficacy of root canal disinfection. Sonic or ultrasonic agitation of irrigants is expected to improve irrigation dynamics. This study examined the effects of microbubble emulsion (ME) combined with sonic or ultrasonic agitation on irrigation dynamics and reduction of biofilm bacteria within root canal models.

METHODS

Two experiments were conducted. First, high-speed imaging was used to characterize the bubble dynamics generated in ME by sonic or ultrasonic agitation within canals of polymer tooth models. Second, 5.25% NaOCl irrigation or ME was sonically or ultrasonically agitated in canals of extracted teeth with 7-day-grown Enterococcus faecalis biofilms. Dentinal shavings from canal walls were sampled at 1 mm and 3 mm from the apical terminus, and colony-forming units (CFUs) were enumerated. Mean log CFU/mL values were analyzed with analysis of variance and post hoc tests.

RESULTS

High-speed imaging demonstrated strongly oscillating and vaporizing bubbles generated within ME during ultrasonic but not sonic agitation. Compared with CFU counts in controls, NaOCl-sonic and NaOCl-ultrasonic yielded significantly lower counts (P < .05) at both measurement levels. ME-sonic yielded significantly lower counts (P = .002) at 3 mm, whereas ME-ultrasonic yielded highly significantly lower counts (P = .000) at both measurement levels. At 3 mm, ME-ultrasonic yielded significantly lower CFU counts (P = .000) than ME-sonic, NaOCl-sonic, and NaOCl-ultrasonic.

CONCLUSIONS

Enhanced bubble dynamics and reduced E. faecalis biofilm bacteria beyond the level achieved by sonic or ultrasonic agitation of NaOCl suggested a synergistic effect of ME combined with ultrasonic agitation.

Selective toxicity of rose bengal to ovarian cancer cells in vitro

Rose bengal (RB) has been utilized as a photodynamic agent for the targeted killing of cancer cells. Recent data suggest that intralesional RB alone may be effective in chemoablating locoregional and metastatic melanomas. The ability of RB to induce direct and bystander melanoma cell death led to the speculation that it may be similarly effective in the treatment of other neoplasms. The objective of this study was to determine whether RB can limit the growth, or kill, ovarian cancer cells in vitro. Ovarian carcinoma cells with or without a germline BRCA1 mutation were cultured with up to 800 μM RB for one hour or four days, after which their ability to proliferate was assessed using the MTT assay. Control cells included an embryonic kidney cell line transformed with adenovirus, and normal human fibroblasts. Ovarian cancer cells exhibited significant dose-dependent suppression of growth in response to RB; this suppression was similar to that seen with carboplatin. RB treated ovarian cancer cells appeared rounded, shrunken, and damaged. RB also inhibited the growth of kidney tumor cells but was much less effective in slowing the growth of normal human fibroblasts suggesting that RB-mediated growth suppression might be tumor cell specific. Ovarian cancer cells treated with RB displayed a significant increase in apoptosis that peaked at approximately four times the levels seen in untreated control cells. Furthermore, RB exposure resulted in the intracellular generation of reactive oxygen species (ROS) at levels that were significantly greater than in untreated cells and similar to levels seen in cells treated short term with H(2)O(2). These data suggest that RB may not only suppress ovarian cancer cell growth but also induce their apoptotic cell death, justifying the further investigation of the effects of RB in an animal model of ovarian cancer.

Strategies to potentiate antimicrobial photoinactivation by overcoming resistant phenotypes

Conventional antimicrobial strategies have become increasingly ineffective due to the emergence of multidrug resistance among pathogenic microorganisms. The need to overcome these deficiencies has triggered the exploration of alternative treatments and unconventional approaches towards controlling microbial infections. Photodynamic therapy (PDT) was originally established as an anticancer modality and is currently used in the treatment of age-related macular degeneration. The concept of photodynamic inactivation requires cell exposure to light energy, typically wavelengths in the visible region that causes the excitation of photosensitizer molecules either exogenous or endogenous, which results in the production of reactive oxygen species (ROS). ROS produce cell inactivation and death through modification of intracellular components. The versatile characteristics of PDT prompted its investigation as an anti-infective discovery platform. Advances in understanding of microbial physiology have shed light on a series of pathways, and phenotypes that serve as putative targets for antimicrobial drug discovery. Investigations of these phenotypic elements in concert with PDT have been reported focused on multidrug efflux systems, biofilms, virulence and pathogenesis determinants. In many instances the results are promising but only preliminary and require further investigation. This review discusses the different antimicrobial PDT strategies and highlights the need for highly informative and comprehensive discovery approaches.

Microbial efflux pump inhibition: tactics and strategies

Traditional antimicrobials are increasingly suffering from the emergence of multidrug resistance among pathogenic microorganisms. To overcome these deficiencies, a range of novel approaches to control microbial infections are under investigation as potential alternative treatments. Multidrug efflux is a key target of these efforts. Efflux mechanisms are broadly recognized as major components of resistance to many classes of chemotherapeutic agents as well as antimicrobials. Efflux occurs due to the activity of membrane transporter proteins widely known as Multidrug Efflux Systems (MES). They are implicated in a variety of physiological roles other than efflux and identifying natural substrates and inhibitors is an active and expanding research discipline. One plausible alternative is the combination of conventional antimicrobial agents/antibiotics with small molecules that block MES known as multidrug efflux pump inhibitors (EPIs). An array of approaches in academic and industrial research settings, varying from high-throughput screening (HTS) ventures to bioassay guided purification and determination, have yielded a number of promising EPIs in a series of pathogenic systems. This synergistic discovery platform has been exploited in translational directions beyond the potentiation of conventional antimicrobial treatments. This venture attempts to highlight different tactical elements of this platform, identifying the need for highly informative and comprehensive EPI-discovery strategies. Advances in assay development genomics, proteomics as well as the accumulation of bioactivity and structural information regarding MES facilitates the basis for a new discovery era. This platform is expanding drastically. A combination of chemogenomics and chemoinformatics approaches will integrate data mining with virtual and physical HTS ventures and populate the chemical-biological interface with a plethora of novel chemotypes. This comprehensive step will expedite the preclinical development of lead EPIs.

Photosensitization reactions in vitro and in vivo

This review of Photochemistry and Photobiology summarizes articles published in 2010, and highlights progress in the area of photosensitization. The synthesis of conjugated photosensitizers is an area of interest where increasing water solubility has been a goal. Targeting infrared sensitizer absorption has been another goal, and relates to the practical need of deep tissue absorption of light. Photodynamic techniques for inactivating microbes and destroying tumors have been particularly successful. Biologically, singlet oxygen [(1)O(2)((1)Δ(g))] is an integral species in many of these reactions, although photosensitized oxidations tuned to electron and hydrogen transfer (Type I) give rise to other reactive species, such as superoxide and hydrogen peroxide. How photoprotection against yellowing, oxygenation and degradation occurs was also an area of topical interest.