Rationale and mechanism for the low photoinactivation rate of bacteria in plasma

Contributions of early and mid-level visual cortex to high-level object categorization

The complexity of visual features for which neurons are tuned increases from early to late stages of the ventral visual stream. Thus, the standard hypothesis is that high-level functions like object categorization are primarily mediated by higher visual areas because they require more complex image formats that are not evident in early visual processing stages. However, human observers can categorize images as objects or animals or as big or small even when the images preserve only some low- and mid-level features but are rendered unidentifiable ('texforms', Long et al., 2018). This observation suggests that even the early visual cortex, in which neurons respond to simple stimulus features, may already encode signals about these more abstract high-level categorical distinctions. We tested this hypothesis by recording from populations of neurons in early and mid-level visual cortical areas while rhesus monkeys viewed texforms and their unaltered source stimuli (simultaneous recordings from areas V1 and V4 in one animal and separate recordings from V1 and V4 in two others). Using recordings from a few dozen neurons, we could decode the real-world size and animacy of both unaltered images and texforms. Furthermore, this neural decoding accuracy across stimuli was related to the ability of human observers to categorize texforms by real-world size and animacy. Our results demonstrate that neuronal populations early in the visual hierarchy contain signals useful for higher-level object perception and suggest that the responses of early visual areas to simple stimulus features display preliminary untangling of higher-level distinctions.

Domestic LED bulb induced photodynamic effect of Toluidine Blue O-embedded silicone catheters against urinary tract infection

BACKGROUND

Novel combination of Toluidine Blue O (TBO) embedded silicone catheter with domestic/household LED bulb has a potential in clinical infection such as prevention of multi drug resistant catheter-associated urinary tract infections (CAUTIs) through photodynamic therapy.

MATERIAL AND METHODS

Preliminarily, TBO was entrapped into silicone catheter by swell-encapsulation-shrink method. Further, in vitro study was carried out to check the antimicrobial photodynamic efficacy of TBO with domestic/household LED light. Antibiofilm activity was evaluated by scanning electron microscopy.

RESULTS

The results showed that these modified TBO embedded silicone catheters showed significant antimicrobial and antibiofilm activity against vancomycin resistant Staphylococcus aureus VRSA. Small piece (1 cm) of TBO-embedded silicone catheter (700 µM) showed 6 log₁₀ reduction in the viable count when exposed for only 5 min of domestic/household LED bulb, while 1 cm piece of 500 µM and 700 µM concentration of TBO-embedded catheter eradicated all bacterial load when exposed to 15 min of light. Segment of medical grade TBO-embedded silicone catheters were used to carry out investigation of reactive oxygen species generation mainly singlet oxygen that contributes to type II phototoxicity.

CONCLUSION

These modified catheter provides cost effective, easy to manage and less time consuming therapy to eliminate CAUTIs.

A nano phototheranostic approach of toluidine blue conjugated gold silver core shells mediated photodynamic therapy to treat diabetic foot ulcer

Diabetic foot infection caused by multidrug-resistant bacteria, is becoming serious problem. Moreover, polymicrobial biofilms contribute significantly to the persistent infections. In the present study, we investigated the effectiveness of novel toluidine blue conjugated chitosan coated gold-silver core-shell nanoparticles (TBO-chit-Au-AgNPs) mediated photodynamic therapy and demonstrate their use as a nontoxic antibacterial therapy to combat diabetic foot ulcer (DFU) caused by multi-drug resistant strains both in monomicrobial and polymicrobial state of infection. In vitro efficacy of TBO-chit-Au-AgNPs mediated photodynamic therapy (PDT) against polymicrobial biofilms was determined using standard plate count method and compared with that of monomicrobial biofilms of each species. Different anti-biofilm assays and microscopic studies were performed to check the efficacy of TBO-chit-Au-AgNPs mediated PDT, displayed significant decrease in the formation of biofilm. Finally, its therapeutic potential was validated in vivo type-2DFU. Cytokines level was found reduced, using nano-phototheranostic approach, indicating infection control. Expression profile of growth factors confirmed both the pathogenesis and healing of DFU. Hence, we conclude that TBO-chit-Au-AgNPs mediated PDT is a promising anti-bacterial therapeutic approach which leads to a synergistic healing of DFU caused by MDR bacterial strains.

Antimicrobial photodynamic therapy (aPDT) against vancomycin resistant Staphylococcus aureus (VRSA) biofilm disruption: A putative role of phagocytosis in infection control

Biofilm mediated infections have major clinical impact. Staphylococcus aureus is a pathogen that frequently causes biofilm forming infections, such as those associated with medical devices and persistent wounds. Microorganisms embedded in biofilm are impervious to antibiotics and other antimicrobial agents, thus they are difficult to eliminate. The upsurge of multi-drug resistant strains makes treating such illnesses even more difficult. Therefore, new strategies are required to combat such type of infections. In this work, we have proposed an alternative therapeutic option to eradicate preformed biofilm of vancomycin resistant Staphylococcus aureus (VRSA) and enhanced phagocytosis by neutrophils in fresh human blood using curcumin mediated antimicrobial photodynamic therapy (aPDT).At sub-MIC of curcumin, different anti-biofilm assays and microscopic examinations were performed, followed by 20 J/cm² of blue laser light irradiation which corresponds to 52 s only. The result showed significant disruption of VRSA biofilm. Moreover, when curcumin-aPDT treated VRSA biofilm was exposed to whole blood from healthy donors, it was nearly completely eradicated. The present study suggests that curcumin-aPDT enhanced phagocytosis may be a useful strategy for inactivating VRSA biofilms adhering to medical implant surfaces.

Antimicrobial and antibiofilm photodynamic therapy against vancomycin resistant Staphylococcus aureus (VRSA) induced infection in vitro and in vivo

Biofilm mediated infection caused by multi-drug resistant bacteria are difficult to treat since it protects the microorganisms by host defense system, making them resistant to antibiotics and other antimicrobial agents. Combating such type of nosocomial infection, especially in immunocompromised patients, is an urgent need and foremost challenge faced by clinicians. Therefore, antimicrobial photodynamic therapy (aPDT) has been intensely pursued as an alternative therapy for bacterial infections. aPDT leads to the generation of reactive oxygen species (ROS) that destroy bacterial cells in the presence of a photosensitizer, visible light and oxygen. Here, we elucidated a possibility of its clinical application by reducing the treatment time and exposing curcumin to 20 J/cm² of blue laser light, which corresponds to only 52 s to counteract vancomycin resistant Staphylococcus aureus (VRSA) both in vitro and in vivo. To understand the mechanism of action, the generation of total reactive oxygen species (ROS) was quantified by 2'-7'-dichlorofluorescein diacetate (DCFH-DA) and the type of phototoxicity was confirmed by fluorescence spectroscopic analysis. The data showed more production of singlet oxygen, indicating type-II phototoxicity. Different anti-biofilm assays (crystal violet and congo red assays) and microscopic studies were performed at sub-MIC concentration of curcumin followed by treatment with laser light against preformed biofilm of VRSA. The result showed significant reduction in the preformed biofilm formation. Finally, its therapeutic potential was validated in skin abrasion wistar rat model. The result showed significant inhibition of bacterial growth. Furthermore, immunomodulatory analysis with rat serum was performed. A significant reduction in expression of proinflammatory cytokines TNF-α and IL-6 were observed. Hence, we conclude that curcumin mediated aPDT with 20 J/cm² of blue laser treatment (for 52 s) could be used against multi-drug resistant bacterial infections and preformed biofilm formation as a potential therapeutic approach.

Curcumin induced photodynamic therapy mediated suppression of quorum sensing pathway of Pseudomonas aeruginosa: An approach to inhibit biofilm in vitro

OBJECTIVE

The objective of this study was to inhibit the Pseudomonas aeruginosa biofilm through curcumin-mediated antimicrobial photodynamic therapy (A-PDT).

BACKGROUND

The mechanism behind A-PDT mediated photoinactivation depend upon reactive oxygen species (ROS) production, like singlet oxygen and free radicals.

METHODS

To evaluate the antibacterial efficacy of curcumin induced A-PDT on P. aeruginosa by colony forming unit (CFU) while antibiofilm action was determined by the use of crystal violet, XTT, congored binding assay and confocal laser scanning microscope (CLSM).

RESULTS

We found that curcumin with 10 J/cm² of light reduces P. aeruginosa biofilm more efficiently than without light. Extracellular polymeric substances (EPS) production was also reduced by approx 94 % with 10 J/cm² of light dose. CLSM images showed that the thickness of biofilms were reduced from >30 μm to <5 μm after treatment with curcumin followed by 10 J/cm² of light irradiation. Curcumin showed better bacteriostatic activity than bactericidal activity. Singlet oxygen is primarily responsible for photodamage and cytotoxic reactions caused by curcumin-mediated APDT. Genes involved in quorum sensing (QS) pathway was also found to be inhibited after APDT. Curcumin with 5 J/cm² light inhibits QS genes and on increasing light dose i.e10 J/cm², we found a drastic reduction in gene expression.

CONCLUSION

We conclude that the curcumin mediated A-PDT inhibits biofilm formation ofP. aeruginosa through QS pathway by the action of singlet oxygen generation which in turn reduced EPS of the biofilm.

Determining and unravelling origins of reduced photoinactivation efficacy of bacteria in milk

Bovine mastitis is an endemic disease of dairy cattle that is considered to be one of the most frequent and costly diseases in veterinary medicine. An increase in the incidence of disease results in the increased use of antibiotics, which in turn increases the potential of bacterial resistance. This study aimed to investigate the effectiveness of antimicrobial photodynamic therapy (aPDT) in the treatment of bovine mastitis, as an alternative to systemic antibiotics. To identify the key factors affecting photoinactivation efficacy, realistic experiments in view of the end-use were conducted in milk samples using two different photosensitizers: methylene blue (MB) and silicon (IV) phthalocyanine derivative (SiPc). We explored the effects of divalent ions and fat content on the aPDT outcome and determined influence of different proteins on aPDT efficacy. Levels of bacterial sensitivity to PSs varied depending on the type of bacteria (Gram-positive vs. Gram-negative) and light exposure time. Critical interrelated factors affecting aPDT in milk were identified and an efficient combination of treatment conditions that can lead to a full photodynamic inactivation of bacteria was determined.

Efficacy of photodynamic therapy against Streptococcus mutans biofilm: Role of singlet oxygen

In photodynamic therapy (PDT), killing is entirely based on the ROS generation and among different types of ROS generated during PDT, singlet oxygen is considered as the most potential as illustrated in many studies and therefore it is predominantly responsible for photodamage and cytotoxic reactions. The aim of this study was to check whether singlet oxygen (Type II photochemistry) is more potential than free radicals (Type I photochemistry) against Streptococcus mutans biofilm. We have taken two phenothiazinium dyes i.e. toluidine blue O (TBO) and new methylene blue (NMB). TBO was found to have better antibacterial as well as antibiofilm effect than NMB. Antibacterial effect was evaluated by colony forming unit while antibiofilm action by crystal violet and congo red binding assays. We have also evaluated the disruption of preformed biofilm by biofilm reduction assay, confocal laser electron and scanning electron microscopy. More singlet oxygen production was detected in case of TBO than NMB while more Free radical (HO) was produced by NMB than TBO. TBO showed better antibacterial as well as antibiofilm effect than NMB so; we conclude that potency of a photosensitizer is correlated with the capability to produce singlet oxygen.

Enhanced photodynamic therapy using light fractionation against Streptococcus mutans biofilm: type I and type II mechanism

AIM

The objective of the study was to look the efficacy of fractionated light against Streptococcus mutans biofilm.

MATERIALS & METHODS

Antibiofilm assays (crystal violet, congo red), electron microscopic, confocal and spectroscopic studies were performed to check the effect of fractionated light.

RESULTS

6-6.5 log₁₀ reduction of planktonic and 3.6-4.2 log₁₀ reduction in biofilm were observed after irradiation with fractionated as compared with continuous light. Increased permeability to propidium iodide and leakage of cellular constituent validate the greater antibiofilm effect of fractionated light. Spectroscopic studies confirmed the relative contribution of type I and type II photochemistry.

CONCLUSION

Phenothiazinium dyes have a potential against bacterial biofilm in combination with light fractionation and it offers new opportunities to explore its clinical implication.

Aluminum plasmonic nanoshielding in ultraviolet inactivation of bacteria

Ultraviolet (UV) irradiation is an effective bacterial inactivation technique with broad applications in environmental disinfection. However, biomedical applications are limited due to the low selectivity, undesired inactivation of beneficial bacteria and damage of healthy tissue. New approaches are needed for the protection of biological cells from UV radiation for the development of controlled treatment and improved biosensors. Aluminum plasmonics offers attractive opportunities for the control of light-matter interactions in the UV range, which have not yet been explored in microbiology. Here, we investigate the effects of aluminum nanoparticles (Al NPs) prepared by sonication of aluminum foil on the UVC inactivation of E. coli bacteria and demonstrate a new radiation protection mechanism via plasmonic nanoshielding. We observe direct interaction of the bacterial cells with Al NPs and elucidate the nanoshielding mechanism via UV plasmonic resonance and nanotailing effects. Concentration and wavelength dependence studies reveal the role and range of control parameters for regulating the radiation dosage to achieve effective UVC protection. Our results provide a step towards developing improved radiation-based bacterial treatments.

Synergistic reaction of silver nitrate, silver nanoparticles, and methylene blue against bacteria

In this paper we describe the antibacterial effect of methylene blue, MB, and silver nitrate reacting alone and in combination against five bacterial strains including Serratia marcescens and Escherichia coli bacteria. The data presented suggest that when the two components are combined and react together against bacteria, the effects can be up to three orders of magnitude greater than that of the sum of the two components reacting alone against bacteria. Analysis of the experimental data provides proof that a synergistic mechanism is operative within a dose range when the two components react together, and additive when reacting alone against bacteria.

The low photo-inactivation rate of bacteria in human plasma II. Inhibition of methylene blue bleaching in plasma and effective bacterial destruction by the addition of dilute acetic acid to human plasma

Bacteria in human plasma resist methylene blue photo-inactivation. The addition of dilute acetic acid prevents MB bleaching and restores the efficient destruction of bacteria.

Photosensitisation studies of silicone polymer doped with methylene blue and nanogold for antimicrobial applications

2 nm gold nanoparticle (AuNP) and methylene blue (MB) incorporated into medical-grade silicone polymer for antimicrobial applications.

A bivalent cationic dye enabling selective photo-inactivation against Gram-negative bacteria

Selective photoinactivation against Gram-negative bacteria over Gram-positive bacteria was successfully realized by a bivalent triarylmethane dye.