Rose Bengal located within liposome do not affect the activity of inside-out oriented Na,K-ATPase

DPPC:DPPE-proteoliposomes (in which the enzyme is inside-out oriented) and DLOPC:DLOPE-proteoliposomes (in which the enzyme is only 40% inside-out oriented) is an excellent model for studying the selective effect of the reactive oxygen species, produced by the photo-activation of Rose Bengal. Both proteoliposomes used, when submitted to photo-irradiation with laser using 1200 mJ/cm2 energy dose, in the absence of the Rose Bengal, did not shown any effect in the ATPase activity and in the integrity of its systems. Also, no effect was observed using 50 microM of Rose Bengal encapsulated in the interior of the DPPC:DPPE-proteoliposome system. But, when we use 50 microM of Rose Bengal, present only in the extravesicular environment, and photo-irradiation with a laser dose of 200 mJ/cm2, it results in the loss of 40-50% of the ATPase activity, with damage of the DPPC:DPPE-proteoliposome integrity. Using a dose of 400 mJ/cm2 the ATPase activity was totality lost. Consequently, these effects could be correlated with direct damage in the peptide structure. The photo-irradiation of the system constituted by DLOPC:DLOPE-proteoliposome in the presence of Rose Bengal, encapsulated only in the interior compartment or in the extra-liposomal environments, revealed a gradual decrease of the ATPase activity, maintaining it at 30% after a dose of 1200 mJ/cm2 and losing total ATPase activity at 800 mJ/cm2, respectively, with the loss of integrity of this vesicular system in both conditions studied. The generated singlet oxygen could attack the double linkage present in the fatty acid structure of the lipid instead of the amino acid in the protein structure and, in a second step, result in an indirect inactivation of the enzyme activity. In summary, these results indicated that singlet oxygen species produced by photo-oxidation of Rose Bengal using laser light could act in protein and lipid structure depending on its proportion or distribution.     

Reactivities of diphenylfuran (a singlet oxygen trap) with singlet oxygen and hydroxyl radical in aqueous systems.

It has been studied whether 2,5-diphenylfuran is a specific singlet oxygen trap in aqueous systems. With certain ¹O₂ generating systems (Rose Bengal photooxygenation and NaOClH₂O₂ systems) and·OH generating systems (Fenton's reagent and acetaldehyde-xanthine oxidase system), diphenylfuran was chiefly converted in all cases to cis-dibenzoyl-ethylene, but not to trans-dibenzoylethylene. Low but detectable conversion of diphenylfuran to a hydroperoxide, probably a distinct ¹O₂-derived reaction in aqueous media, was found only in the Rose Bengal photooxygenation system.     

Lipid-mediated regulation of pore-forming activity of syringomycin E by thyroid hormones and xanthene dyes

The effects of dipole modifiers, thyroid hormones (thyroxine and triiodothyronine) and xanthene dyes (Rose Bengal, phloxineB, erythrosin, eosinY and fluorescein) on the pore-forming activity of the lipopeptide syringomycin E (SRE) produced by Pseudomonas syringae were studied in a model bilayer. Thyroxine does not noticeably influence the steady-state number of open SRE channels (N_op), whereas triiodothyronine decreases it 10-fold at − 50 mV. Rose Bengal, phloxine B and erythrosin significantly increase N_op by 350, 100 and 70 times, respectively. Eosin Y and fluorescein do not practically affect the pore-forming activity of SRE. Recently, we showed that hormones decrease the dipole potential of lipid bilayers by approximately 60 mV at 50 μM, while Rose Bengal, phloxine B and erythrosin at 2.5 μM reduce the membrane dipole potential by 120, 80 and 50 mV, respectively. In the present study using differential scanning microcalorimetry, confocal fluorescence microscopy, the calcein release technique and measurements of membrane curvature elasticity, we show that triiodothyronine strongly affects the fluidity of model membranes: its addition leads to a significant decrease in the temperature and cooperativity of the main phase transition of DPPC, calcein leakage from DOPC vesicles, fluidization of solid domains in DOPC/DPPC liposomes, and promotion of lipid curvature stress. Thyroxine exerts a weaker effect. Xanthene dyes do not influence the phase transition of DPPC. Despite the decrease in the dipole potential, thyroid hormones modulate SRE channels predominantly via the elastic properties of the membrane, whereas the xanthene dyes Rose Bengal, phloxine B and erythrosine affect SRE channels via bilayer electrostatics.     

Photodynamic Effects of Rose Bengal on Senescent Flax Cotyledons

Senescent cotyledons, excised intact from 6-d-old Flax (Linumusitatissium) seedlings, were treated with Rose Bengal, a photo-sensitizingagent. In continuous light, chlorophyll breakdown was increasedfrom 44% in untreated cotyledons to 73% in Rose Bengal-treatedcotyledons. Depletion of carotenoid and linolenic acid was enhancedby 25% and 39% respectively over the same period. After 48 hthe decline in uncoupled photosynthetic electron transport wasincreased from 58% to 82% in isolated chloroplasts. Over thesame period CO₂ exchange was greatly inhibited in treated cotyledons.Rose Bengal had little effect on dark incubated cotyledons,suggesting that singlet oxygen generated by photo-sensitizedreactions was responsible for the enhanced deterioration ofstructure and function of senescent cotyledons and the primesite of action was the photosynthesis apparatus. These photodynamiceffects are discussed in relation to the possible involvementof toxic oxygen species in the senescence of leaf tissue. Key words: Senescence, Photodynamic damage, Rose Bengal, Singlet oxygen     

Mechanisms of Rose Bengal inhibition on SecA ATPase and ion channel activities

SecA is an essential protein possessing ATPase activity in bacterial protein translocation for which Rose Bengal (RB) is the first reported sub-micromolar inhibitor in ATPase activity and protein translocation. Here, we examined the mechanisms of inhibition on various forms of SecA ATPase by conventional enzymatic assays, and by monitoring the SecA-dependent channel activity in the semi-physiological system in cells. We build on the previous observation that SecA with liposomes form active protein-conducting channels in the oocytes. Such ion channel activity is enhanced by purified Escherichia coli SecYEG–SecDF·YajC liposome complexes. Inhibition by RB could be monitored, providing correlation of in vitro activity and intact cell functionality. In this work, we found the intrinsic SecA ATPase is inhibited by RB competitively at low ATP concentration, and non-competitively at high ATP concentrations while the translocation ATPase with precursors and SecYEG is inhibited non-competitively by RB. The Inhibition by RB on SecA channel activity in the oocytes with exogenous ATP-Mg²⁺, mimicking translocation ATPase activity, is also non-competitive. The non-competitive inhibition on channel activity has also been observed with SecA from other bacteria which otherwise would be difficult to examine without the cognate precursors and membranes.     

An in vitro study of the photodynamic effect of rose bengal on trichophyton rubrum

Onychomycosis, a fungal infection of the finger or toenails, is predominantly caused by Trichophyton rubrum. Treatment is difficult due to high recurrence rates and problems with treatment compliance. For these reasons, alternative therapies are needed. Here we describe the photoactivation of Rose Bengal (RB) using a green laser (λ = 532 nm) at fluences of 68, 133 and 228 J/cm², and assess its fungicidal activity on T. rubrum spore suspensions. A 140 µM RB solution was able to induce a fungicidal effect on T. rubrum when photosensitized with the fluence of 228 J/cm². RB photosensitization using a green laser provides a potential novel treatment for T. rubrum infections. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Visible-light promoted degradation of the commercial antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT): a kinetic study

Abstract

Visible-light photo-irradiation of the commercial phenolic antioxidants (PhAs) butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), in the presence of vitamin B₂ (riboflavin, Rf), in methanolic solutions and under aerobic conditions, results in the photo-oxidation of the PhAs. The synthetic dye photosensitiser Rose Bengal was also employed for auxiliary experiments. With concentrations of riboflavin and PhAs of ca. 0.02 mM and < 1 mM, respectively, the excited triplet state of the vitamin (³Rf*) is quenched by BHT in a competitive fashion with dissolved ground state triplet oxygen. From the quenching of ³Rf*, the semireduced form of the pigment is generated through an electron transfer process from BHT, with the subsequent production of superoxide anion radical (O₂^??) by reaction with dissolved molecular oxygen. In parallel, the species singlet molecular oxygen, O₂(¹Δ_g), is also generated. Both reactive oxygen species produce the photodegradation of BHT. In the case of BHA, the lack of any effect exerted by superoxide dismutase drives out a significant participation of a O₂^??-mediated mechanism. BHA mainly interacts with O₂(¹Δ_g) and exhibits a desirable property as an antioxidant – a relatively high capacity for O₂(1Δ_g) de-activation and a low photodegradation efficiency by the oxidative species. Electrochemical determinations support the proposed photodegradative mechanism.     

Role of reactive oxygen species in cardiac preconditioning: Study with photoactivated rose bengal in isolated rat hearts

Oxygen radical scavengers have been shown to prevent the development of ischemic preconditioning, suggesting that reactive oxygen species (ROS) might be involved in this phenomenon. In the present study, we have investigated whether direct exposure to ROS produced by photoactivated Rose Bengal (RB) could mimic the protective effects of ischemic preconditioning.

Methods In vitro generation of ROS from photoactivated RB in a physiological buffer was first characterised by ESR spectroscopy in the presence of 2,2,6,6-tetramethyl-1-piperidone (oxoTEMP) or 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). In a second part of the study, isolated rat hearts were exposed for 2.5 min to photoactivated RB. After 5 min washout, hearts underwent 30 min no-flow normothermic ischemia followed by 30 min of reperfusion.

Results and Conclusions The production of singlet oxygen (¹O₂) by photoactivated RB in the perfusion medium was evidenced by the ESR detection of the nitroxyl radical oxoTEMPO. Histidine completely inhibited oxoTEMPO formation. In addition, the use of DMPO has indicated that (i) superoxide anions (O^·-₂) are produced directly and (ii) hydroxyl radicals (HO^·) are formed indirectly from the successive O^·-₂ dismutation and the Fenton reaction. In the perfusion experiments, myocardial post-ischemic recovery was dramatically impaired in hearts previously exposed to the ROS produced by RB photoactivation (¹O₂, O^·-₂, H₂O₂ and HO^·) as well as when ¹O₂ was removed by histidine (50 mM) addition. However, functional recovery was significantly improved when hearts were exposed to photoactivated RB in presence of superoxide dismutase (10⁵ IU/L) and catalase (10⁶ IU/L).

Further studies are now required to determine whether the cardioprotective effects of Rose Bengal in presence of O^·-₂ and H₂O₂ scavengers are due to singlet oxygen or to other species produced by Rose Bengal degradation.     

On the amino acids involved in the ATPase site of mitochondrial F1 and the implication of the subunit C.

The data on the pH dependence of the K_m for Mg-ATP and the V_m of the ATPase of pig heart mitochondrial F₁ indicate the presence of two groups of different pK's which modify the enzyme activity. The first pK at pH 9.6 ± 0.2 may be related to the possible presence of arginine and/or tyrosine residues in the ATPase site; the second pK at pH 7.2 ± 0.2 could be due to the presence of a histidine residue in the ATPase site or to the involvement of amino groups in the ATPase site. The inhibition induced by photooxidation in the presence of Rose Bengal is not pH dependent in the pH range corresponding to the pK of histidine. The inhibition induced by diethylpyrocarbonate cannot be reversed by hydroxylamine and the characteristics of this inhibition rather correspond to the reaction of the inhibitor with amino groups. Pyridoxal phosphate also inhibits the ATPase activity of F₁ by reaction with amino groups. The presence of ATP or phosphate partially protects against the inhibition induced by diethylpyrocarbonate or pyridoxal phosphate, which indicates that amino groups may be directly or indirectly involved in the binding of nucleotide and phosphate to F₁. Glutaraldehyde also inhibits the enzyme by reacting with amino groups and inducing a crosslinking of the subunits. The disappearance of subunit C is well correlated with the decrease of ATPase activity, indicating that subunit C is essential in the ATPase activity.     

Efficient singlet oxygen inactivation of firefly luciferase

Firefly luciferase is inactivated by singlet oxygen at near diffusion controlled rates, 1.9 X 10(9) M-1 s-1, based on direct comparison with the oxidation of L-histidine. The inactivation kinetics are multiphasic. Inactivation is inhibitable by NaN3. Surface-separated-sensitizer (SSS) system in which singlet oxygen is produced above an air gap separating the reaction solution from the Rose Bengal sensitizer, ensuring only Type II reactions, was compared with a Sensitox II system in which the polymer bound Rose Bengal is contained in the reaction solution and both Type I and Type II reactions can occur. A slight stabilization is afforded by MgSO4.     

Effect of intermittency factor on singlet oxygen and PGE2 formation in azulene-mediated photodynamic therapy: A preliminary study

In photodynamic therapy, intermittent irradiation modes that incorporate an interval between pulses are believed to decrease the effect of hypoxia by permitting an interval of re-oxygenation. The effect of the irradiation intermittency factor (the ratio of the irradiation pulse time to the total irradiation time) on singlet oxygen formation and inflammatory cytokine production was examined using azulene as a photosensitizer. Effects of difference intermittency factor on singlet oxygen formation and inflammatory cytokine were examined. Azulene solutions (1/10 μM) were irradiated with a 638-nm 500 mW diode laser in fractionation (intermittency factor of 5 or 9) or continuous mode using 50 mW/cm² at 4 or 8 J/cm². Singlet oxygen measurement was performed using a dimethyl anthracene probe. Peripheral blood mononuclear cells (PBMC) were stimulated by 10 ng/ml rhTNF-α for 6 h, before addition of 1 and 10 μM azulene solutions and irradiation. PGE₂ measurement was undertaken using a human PGE₂ ELISA kit. Kruskal-Wallis with Dunn Bonferroni test was used for statistical analyses at p < 0.05.Irradiation of 1 μM azulene+4 J/cm²+intermittency factor of 9 increased singlet oxygen 3-fold (p < 0.0001). Irradiation of 10 μM azulene at either 4 J/cm²+intermittency of 9 or 8 J/cm²+intermittency factor of 5 reduced PGE₂ expression in PBMCs to non-inflamed levels. Thus, at 50 mW/cm², 10 μM azulene-mediated photodynamic therapy with a high intermittency factor and a low energy density generated sufficient singlet oxygen to suppress PGE₂ in Inflamed PBMCs.     

Quenching of singlet oxygen by alkaloids and related nitrogen heterocycles

Fifteen plant alkaloids and related heterocyclic compounds were tested for their ability to quench singlet oxygen. Most of the compounds showed high activity; brucine and strychnine were especially efficient quenchers. Brucine, at a concentration of ca 2.6 x 10^?5 M, is capable of inactivating half the singlet oxygen molecules it encounters. This quenching may serve in nature to protect plants from the deleterious effects of singlet oxygen or other reactive oxidants.     

Iso-mukaadial acetate and ursolic acid acetate inhibit the chaperone activity of Plasmodium falciparum heat shock protein 70-1

Plasmodium falciparum is the most lethal malaria parasite. The present study investigates the interaction capabilities of select plant derivatives, iso-mukaadial acetate (IMA) and ursolic acid acetate (UAA), against P. falciparum Hsp70-1 (PfHsp70-1) using in vitro approaches. PfHsp70-1 facilitates protein folding in the parasite and is deemed a prospective antimalarial drug target. Recombinant PfHsp70-1 protein was expressed in E. coli BL21 cells and homogeneously purified by affinity chromatography. The interaction between the compounds and PfHsp70-1 was evaluated using malate dehydrogenase (MDH), and luciferase aggregation assay, ATPase activity assay, and Fourier transform infrared (FTIR). PfHsp70-1 prevented the heat-induced aggregation of MDH and luciferase. However, the PfHsp70-1 chaperone role was inhibited by IMA or UAA, leading to both MDH and luciferase’s thermal aggregation. The basal ATPase activity of PfHsp70-1 (0.121 nmol/min/mg) was closer to UAA (0.131 nmol/min/mg) (p = 0.0675) at 5 mM compound concentration, suggesting that UAA has no effect on PfHsp70-1 ATPase activity. However, ATPase activity inhibition was similar between IMA (0.068 nmol/min/mg) (p < 0.0001) and polymyxin B (0.083 nmol/min/mg) (p < 0.0001). The lesser the Pi values, the lesser ATP hydrolysis observed due to compound binding to the ATPase domain. FTIR spectra analysis of IMA and UAA resulted in PfHsp70-1 structural alteration for β-sheets shifting the amide I band from 1637 cm⁻¹ to 1639 cm⁻¹, and for α-helix from 1650 cm⁻¹ to 1652 cm⁻¹, therefore depicting secondary structural changes with an increase in secondary structure percentage suggesting that these compounds interact with PfHsp70-1.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12192-021-01212-6.     

Laser intensity and wavelength dependence of Rose-Bengal-photosensitized inhibition of red blood cell acetylcholinesterase

The intensity and wavelength-dependence of Rose-Bengal-mediated photoinhibition of red blood cell acetylcholinesterase has been studied. Irradiation of dye-membrane suspensions with 308 nm laser excitation resulted in enzyme inhibition almost 50% greater than that obtained with 514 nm laser excitation. Sodium azide and argon purging greatly decreased the photosensitized enzyme inhibition at both wavelengths. Although Rose Bengal photosensitized enzyme inhibition more efficiently upon excitation into Sn (308 nm) than into S1 (514 nm), Stern-Volmer analysis of sodium azide quenching data gave similar quenching efficiencies at both wavelengths. Irradiation of dye-membrane suspensions with increasing intensities (Nd:YAG, 532 nm, 40 ps pulse duration) resulted in a decrease in enzyme inhibition. Saturation of the Rose Bengal fluorescence intensity and light transmission occurred with nearly the same intensity-dependence, suggesting that ground-state depletion occurs at the higher intensities. Our results demonstrate that excitation of a sensitizer into higher-lying excited singlet states can result in enhanced sensitizing efficiency. However, attempts to populate such states in Rose Bengal by sequential two-photon absorption using high intensities resulted only in ground-state depletion.     

The effect of low-intensity laser irradiation in the blue, green, and red spectral ranges on healing of experimental skin wounds in rats

The effects of low-intensity laser irradiation in the red (632.8 nm), green (532 nm), and blue (441.2 nm) spectral ranges on wound healing has been studied in rats. The effect of the traditionally used red laser irradiation has been compared with the effect caused by laser irradiation in other spectral ranges, aiming to support the provisional hypothesis that a similar healing effect could be achieved at lower doses of wound irradiation by lasers emitting in the blue and green spectral ranges. The following parameters have been used to characterize healing of the experimental wounds: the functional activity of phagocytes in the wound exudate, which was determined from luminol-dependent chemiluminescence, the phagocyte number; the wound exudates’ antioxidant activity; and the rate of healing, which was determined as the change of the wound surface area. It was found that in all cases the laser irradiation accelerated the healing of wounds. Exposure to red laser irradiation at the dose of 1.5 J/cm²), and to blue or green laser irradiation at a dose of 0.75 J/cm² shortened the time of the wound healing from 22 to 17 and 19 days, respectively. The functional activity of leukocytes in irradiated groups increased by day 5 after surgery, whereas in the control group it decreased. The superoxide dismutase activity increased in all experimental groups by day 5 after surgery. Laser irradiation in the red spectral range at a dose of 1.5 J/cm² resulted in a larger increase in superoxide dismutase activity, as compared to that found after exposure to laser irradiation in the blue and green spectral ranges at a dose of 0.75 J/cm².     

Visible-light promoted degradation of the commercial antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT): a kinetic study

Visible-light photo-irradiation of the commercial phenolic antioxidants (PhAs) butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), in the presence of vitamin B2 (riboflavin, Rf), in methanolic solutions and under aerobic conditions, results in the photo-oxidation of the PhAs. The synthetic dye photosensitiser Rose Bengal was also employed for auxiliary experiments. With concentrations of riboflavin and PhAs of ca. 0.02 mM and < 1 mM, respectively, the excited triplet state of the vitamin (3Rf*) is quenched by BHT in a competitive fashion with dissolved ground state triplet oxygen. From the quenching of 3Rf*, the semireduced form of the pigment is generated through an electron transfer process from BHT, with the subsequent production of superoxide anion radical (O2*-) by reaction with dissolved molecular oxygen. In parallel, the species singlet molecular oxygen, O2(1delta(g)), is also generated. Both reactive oxygen species produce the photodegradation of BHT. In the case of BHA, the lack of any effect exerted by superoxide dismutase drives out a significant participation of a O2(*-)-mediated mechanism. BHA mainly interacts with O2(1delta(g)) and exhibits a desirable property as an antioxidant--a relatively high capacity for O2(1delta(g)) de-activation and a low photodegradation efficiency by the oxidative species. Electrochemical determinations support the proposed photodegradative mechanism.     

The interactions of Rose Bengal and other aromatic anionic dyes with mannitol-1-phosphate dehydrogenase fromEscherichia coli

The interaction of Rose Bengal with mannitol-1-phosphate dehydrogenase has been investigated. Binding of this aromatic anionic dye causes a quenching of the protein fluorescence and various changes in the spectral properties of the dye. As is the case with other dehydrogenases, the titration of the enzyme with Rose Bengal, monitoring enhancement in the dye fluorescence at 590 nm, or quenching of the protein fluorescence, can be described by a simple binding model: one dye binding site per enzyme subunit with a dissociation constant of ～2 µM. However, kinetic studies indicate a more complex scheme, since Rose Bengal induces a biphasic time-dependent inhibition of the enzyme. The first phase is over in 1–5 min and is partially reversible, while the second phase is essentially irreversible and continues beyond 1 h. The dyes 8-anilino-1-naphthalene sulfonate and 2-p-toluidinylnaphthalene-6-sulfonate also cause biphasic time-dependent inhibitions of the enzyme. Only mannitol-1-phosphate, and fructose-6-phosphate in the presence of NAD⁺, show high levels of protection against these inhibitory processes. The different effects of coenzymes and substrates on the dye-induced inhibitions support earlier observations from fluorescence studies (preceding paper). A binding scheme describing the interactions of Rose Bengal with the enzyme that is consistent with the experimental results is presented.     

Effective photodynamic treatment of Trichophyton species with Rose Bengal

Photodynamic therapy (PDT) with Rose Bengal has previously achieved eradication of Trichophyton rubrum infections causing toenail onychomycosis; however, its antifungal activity against other clinically relevant dermatophytes has yet to be studied. Here, we test the efficacy of PDT using Rose Bengal (140 μM) and 532 nm irradiation (101 J/cm²) against Trichophyton mentagrophytes and Trichophyton interdigitale spores, in comparison to T. rubrum. A significant reduction (>99%) of T. mentagrophytes and T. interdigitale was observed, while actual eradication of viable T. rubrum was achieved (99.99%). Laser irradiation alone inhibited growth of T. rubrum (55.2%) and T. mentagrophytes (45.2%) significantly more than T. interdigitale (25.5%) (P = .0086), which may indicate an increased presence of fungal pigments, xanthomegnin and melanin. The findings suggest that Rose Bengal-PDT can act against a broader spectrum of fungal pathogens, and with continued development may be employed in a wider range of clinical antifungal applications.     

Ultraviolet disinfection of Schistosoma mansoni cercariae in water

BackgroundSchistosomiasis is a parasitic disease that is transmitted by skin contact with waterborne schistosome cercariae. Mass drug administration with praziquantel is an effective control method, but it cannot prevent reinfection if contact with cercariae infested water continues. Providing safe water for contact activities such as laundry and bathing can help to reduce transmission. In this study we examine the direct effect of UV light on Schistosoma mansoni cercariae using ultraviolet light-emitting diodes (UV LEDs) and a low-pressure (LP) mercury arc discharge lamp.MethodologyS. mansoni cercariae were exposed to UV light at four peak wavelengths: 255 nm, 265 nm, 285 nm (UV LEDs), and 253.7 nm (LP lamp) using bench scale collimated beam apparatus. The UV fluence ranged from 0–300 mJ/cm² at each wavelength. Cercariae were studied under a stereo-microscope at 0, 60, and 180 minutes post-exposure and the viability of cercariae was determined by assessing their motility and morphology.ConclusionVery high UV fluences were required to kill S. mansoni cercariae, when compared to most other waterborne pathogens. At 265 nm a fluence of 247 mJ/cm² (95% confidence interval (CI): 234–261 mJ/cm²) was required to achieve a 1-log₁₀ reduction at 0 minutes post-exposure. Cercariae were visibly damaged at lower fluences, and the log reduction increased with time post-exposure at all wavelengths. Fluences of 127 mJ/cm² (95% CI: 111–146 mJ/cm²) and 99 mJ/cm² (95% CI: 85–113 mJ/cm²) were required to achieve a 1-log₁₀ reduction at 60 and 180 minutes post-exposure at 265 nm. At 0 minutes post-exposure 285 nm was slightly less effective, but there was no statistical difference between 265 nm and 285 nm after 60 minutes. The least effective wavelengths were 255 nm and 253.7 nm. Due to the high fluences required, UV disinfection is unlikely to be an energy- or cost-efficient water treatment method against schistosome cercariae when compared to other methods such as chlorination, unless it can be demonstrated that UV-damaged cercariae are non-infective using alternative assay methods or there are improvements in UV LED technology.     

Using UVC Light-Emitting Diodes at Wavelengths of 266 to 279 Nanometers To Inactivate Foodborne Pathogens and Pasteurize Sliced Cheese

UVC light is a widely used sterilization technology. However, UV lamps have several limitations, including low activity at refrigeration temperatures, a long warm-up time, and risk of mercury exposure. UV-type lamps only emit light at 254 nm, so as an alternative, UV light-emitting diodes (UV-LEDs) which can produce the desired wavelengths have been developed. In this study, we validated the inactivation efficacy of UV-LEDs by wavelength and compared the results to those of conventional UV lamps. Selective media inoculated with Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes were irradiated using UV-LEDs at 266, 270, 275, and 279 nm in the UVC spectrum at 0.1, 0.2, 0.5, and 0.7 mJ/cm², respectively. The radiation intensity of the UV-LEDs was about 4 μW/cm², and UV lamps were covered with polypropylene films to adjust the light intensity similar to those of UV-LEDs. In addition, we applied UV-LED to sliced cheese at doses of 1, 2, and 3 mJ/cm². Our results showed that inactivation rates after UV-LED treatment were significantly different (P < 0.05) from those of UV lamps at a similar intensity. On microbiological media, UV-LED treatments at 266 and 270 nm showed significantly different (P < 0.05) inactivation effects than other wavelength modules. For sliced cheeses, 4- to 5-log reductions occurred after treatment at 3 mJ/cm² for all three pathogens, with negligible generation of injured cells.