Membrane damage can be a significant factor in the inactivation of Escherichia coli by near-ultraviolet radiation

Antibacterial Activity of Caffeic Acid Combined with UV-A Light against Escherichia coli O157:H7, Salmonella enterica Serovar Typhimurium, and Listeria monocytogenes

The aim of this study was to evaluate the antibacterial activity of caffeic acid (CA), which is a natural polyphenol, combined with UV-A light against the representative foodborne bacteria Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes. Data regarding the inactivation of these bacteria and its dependence on CA concentration, light wavelength, and light dose were obtained. E. coli O157:H7 and Salmonella Typhimurium were reduced to the detection limit when treated with 3 mM CA and UV-A for 3 J/cm² and 4 J/cm², respectively, and 5 J/cm² treatment induced 3.10 log reduction in L. monocytogenes. To investigate the mechanism for inactivation of Salmonella Typhimurium and L. monocytogenes, measurement of polyphenol uptake, membrane damage assessment, enzymatic activity assay, and transmission electron microscopy (TEM) were conducted. It was revealed that CA was significantly (P < 0.05) absorbed by bacterial cells, and UV-A light allowed a higher uptake of CA for both pathogens. Additionally, CA plus UV-A treatment induced significant (P < 0.05) cell membrane damage. In the enzymatic activity assay, the activities of both pathogens were reduced by CA, and a greater reduction occurred by use of CA plus UV-A. Moreover, transmission electron microscopy (TEM) images indicated that CA plus UV-A treatment notably destroyed the intercellular structure. In addition, antibacterial activity was also observed in commercial apple juice, which showed results similar to those obtained from phosphate-buffered saline (PBS), resulting in a significant (P < 0.05) reduction for all three pathogens without any changes in color parameters (L*, a*, and b*), total phenolic compounds, and DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging activity. IMPORTANCE Photodynamic inactivation (PDI), which involves photoactivation of a photosensitizer (PS), is an emerging field of study, as it effectively reduces various kinds of microorganisms. Although there are several PSs that have been used for PDI, there is a need to find naturally occurring PSs for safer application in the food industry. Caffeic acid, a natural polyphenol found in most fruits and vegetables, has recently been studied for its potential to act as a novel photosensitizer. However, no studies have been conducted regarding its antibacterial activity depending on treatment conditions and its antibacterial mechanism. In this study, we closely examined the effectiveness of caffeic acid in combination with UV-A light for inactivating representative foodborne bacteria in liquid medium. Therefore, the results of this research are expected to be utilized as basic data for future application of caffeic acid in PDI, especially when controlling pathogens in liquid food processing.

Exposure to low doses of UVA increases biofilm formation in Pseudomonas aeruginosa

The establishment of bacterial biofilms on abiotic surfaces is a complex process regulated by multiple genetic regulators and environmental factors which are able to modulate the passage of planktonic cells to a sessile state. Solar ultraviolet-A radiation (UVA, 315-400) is one of the main environmental stress factors that bacteria must face at the Earth´s surface. The deleterious effects of UVA are mainly due to oxidative damage. This paper reports that exposure to low UVA doses promotes biofilm formation in three prototypical strains of Pseudomonas aeruginosa, a relevant opportunistic human pathogen. It demonstrates that exposure of planktonic cells to sublethal doses of UVA can increase cell surface hydrophobicity and swimming motility, two parameters known to favor cell adhesion. These results suggest that UVA radiation acts, at least in part, by promoting the first stages of biofilm development.

Inactivation of Escherichia coli by polychromatic simulated sunlight: evidence for and implications of a fenton mechanism involving iron, hydrogen peroxide, and superoxide

Sunlight inactivation of Escherichia coli has previously been shown to accelerate in the presence of oxygen, exogenously added hydrogen peroxide, and bioavailable forms of exogenously added iron. In this study, mutants unable to effectively scavenge hydrogen peroxide or superoxide were found to be more sensitive to polychromatic simulated sunlight (without UVB wavelengths) than wild-type cells, while wild-type cells grown under low-iron conditions were less sensitive than cells grown in the presence of abundant iron. Furthermore, prior exposure to simulated sunlight was found to sensitize cells to subsequent hydrogen peroxide exposure in the dark, but this effect was attenuated for cells grown with low iron. Mutants deficient in recombination DNA repair were sensitized to simulated sunlight (without UVB wavelengths), but growth in the presence of iron chelators reduced the degree of sensitization conferred by this mutation. These findings support the hypothesis that hydrogen peroxide, superoxide, and intracellular iron all participate in the photoinactivation of E. coli and further suggest that the inactivation rate of enteric bacteria in the environment may be strongly dependent on iron availability and growth conditions.

Solar water disinfection (SODIS): a review from bench-top to roof-top

Solar water disinfection (SODIS) has been known for more than 30 years. The technique consists of placing water into transparent plastic or glass containers (normally 2L PET beverage bottles) which are then exposed to the sun. Exposure times vary from 6 to depending on the intensity of sunlight and sensitivity of the pathogens. Its germicidal effect is based on the combined effect of thermal heating of solar light and UV radiation. It has been repeatedly shown to be effective for eliminating microbial pathogens and reduce diarrhoeal morbidity including cholera. Since 1980 much research has been carried out to investigate the mechanisms of solar radiation induced cell death in water and possible enhancement technologies to make it faster and safer. Since SODIS is simple to use and inexpensive, the method has spread throughout the developing world and is in daily use in more than 50 countries in Asia, Latin America, and Africa. More than 5 million people disinfect their drinking water with the solar disinfection (SODIS) technique. This review attempts to revise all relevant knowledge about solar disinfection from microbiological issues, laboratory research, solar testing, up to and including real application studies, limitations, factors influencing adoption of the technique and health impact.

In situ UVA exposure modulates change in the uptake of radiophosphate in size-fractionated plankton assemblages following UVR exposure

We investigated the effect of ultraviolet radiation (UVR) on the uptake and partitioning of radiophosphate ((33)PO (4) (3-) ) in size-fractionated plankton assemblages (0.2-0.8, 0.8-2.0 and >2.0 μm) collected from nine freshwater lakes located in Saskatchewan, Canada. A significant (p < 0.05) reduction in (33)PO (4) (3-) uptake by plankton was observed in seven of the nine lakes. Plankton >2.0 μm were generally unaffected by UVR, whereas the 0.2-0.8 μm size fraction exhibited severe photoinhibition. The effect of UVR on the 0.8-2.0 μm size fraction was variable, ranging from significant reductions to significant increases in (33)PO (4) (3-) uptake. The >2.0 μm size fraction was composed of a diversity of phytoplankton genera, suggesting that P uptake mechanisms for a range of phytoplankton are resistant to UVR. Our ability to detect a UVR effect on specific plankton size fractions was confounded by the resolution of the analysis. That is, only examining the <2.0 and >2.0 μm size fractions concealed the effect of UVR on plankton <0.8 μm. The magnitude of decrease in P uptake by plankton <0.8 μm was significantly and negatively correlated with in situ UVA exposure. Our results underscore the need for studies to consider both the size resolution of their analysis (i.e., the size of target organisms) and the ambient light conditions under which organisms may have acclimated before generalizing results across limnetic systems.

Survival of Escherichia coli strains in Mediterranean brackish water in the Bizerte lagoon in northern Tunisia

This study investigated survival and virulence of Escherichia coli strains exposed to natural conditions in brackish water. Two E. coli strains (O126:B16 and O55:B5) were incubated in water microcosms in the Bizerte lagoon in northern Tunisia and exposed for 12 days to natural sunlight in June (231 to 386 W/m2, 26 +/- 1 degrees C, 30 g/L) and in April (227 to 330 W/m2, 17 +/- 1 degrees C, 27 g/L) or maintained in darkness for 21 days (17 +/- 1 degrees C, 27 g/L). The results revealed that sunlight was the most significant inactivating factor (decrease of 3 Ulog within 48 hours for the two strains) compared to salinity and temperature (in darkness). Survival time of the strains was prolonged as they were maintained in darkness. Local strain (E. coli O55:B5) showed better survival capacity (T90 = 52 hours) than E. coli O126:B16 (T90 = 11 h). For both, modifications were noted only for some metabolic activities of carbohydrates hydrolysis. Cytotoxicity of the two strains, tested on Vero cell, was maintained during the period of survival.

The respiratory chain is the cell's Achilles' heel during UVA inactivation in Escherichia coli

Solar disinfection (SODIS) is used as an effective and inexpensive tool to improve the microbiological quality of drinking water in developing countries where no other means are available. Solar UVA light is the agent that inactivates bacteria during the treatment. Damage to bacterial membranes plays a crucial role in the inactivation process. This study showed that even slightly irradiated cells (after less than 1 h of simulated sunlight) were strongly affected in their ability to maintain essential parts of their energy metabolism, in particular of the respiratory chain (activities of NADH oxidase, succinate oxidase and lactate oxidase were measured). The cells' potential to generate ATP was also strongly inhibited. Many essential enzymes of carbon metabolism (glucose-6-phosphate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase and malate dehydrogenase) and defence against oxidative stress (catalases and glutathione-disulfide reductase) were reduced in their activity during SODIS. The work suggests that damage to membrane enzymes is a likely cause of membrane dysfunction (loss of membrane potential and increased membrane permeability) during UVA irradiation. In this study, the first targets on the way to cell death were found to be the respiratory chain and F1F0 ATPase.

Sunlight inactivation of enterococci and fecal coliforms in sewage effluent diluted in seawater

Inactivation (loss of culturability) by sunlight of enterococci and fecal coliforms within sewage effluent diluted in seawater was investigated in field experiments. In most experiments, 500-ml flasks of pure silica were used to confine activated sludge effluent diluted to 2% (vol/vol) in seawater. Inactivation of bacteria in these flasks (diameter, 0.1 m) was faster than in either open chambers (depth, 0.25 m) or patches of dyed effluent (depth of order, 1 m), probably because of the longer light paths in the latter two types of experiment, which caused greater attenuation of sunlight. Inactivation of 90% of enterococci generally required 2.3 times the insolation required for 90% inactivation of fecal coliforms, because of both the presence of larger initial shoulders on survival curves and a lower final inactivation rate. Two parameters are required to model inactivation of enterococci, a shoulder constant as well as a rate coefficient. The depth dependence of inactivation rate for both fecal indicators matched the attenuation profile of UV-A radiation at about 360 nm. Inactivation by UV-B radiation (290 to 320 nm), which penetrates much less into seawater, is of minor importance compared with the UV-A and visible radiation in sunlight, contrary to expectations in consideration of published action spectra for bacterial inactivation.

Sunlight inactivation of fecal indicator bacteria and bacteriophages from waste stabilization pond effluent in fresh and saline waters

Sunlight inactivation in fresh (river) water of fecal coliforms, enterococci, Escherichia coli, somatic coliphages, and F-RNA phages from waste stabilization pond (WSP) effluent was compared. Ten experiments were conducted outdoors in 300-liter chambers, held at 14C (mean river water temperature). Sunlight inactivation (k(S)) rates, as a function of cumulative global solar radiation (insolation), were all more than 10 times higher than the corresponding dark inactivation (k(D)) rates in enclosed (control) chambers. The overall k(S) ranking (from greatest to least inactivation) was as follows: enterococci > fecal coliforms greater-than-or-equal E. coli > somatic coliphages > F-RNA phages. In winter, fecal coliform and enterococci inactivation rates were similar but, in summer, enterococci were inactivated far more rapidly. In four experiments that included freshwater-raw sewage mixtures, enterococci survived longer than fecal coliforms (a pattern opposite to that observed with the WSP effluent), but there was little difference in phage inactivation between effluents. In two experiments which included simulated estuarine water and seawater, sunlight inactivation of all of the indicators increased with increasing salinity. Inactivation rates in freshwater, as seen under different optical filters, decreased with the increase in the spectral cutoff (50% light transmission) wavelength. The enterococci and F-RNA phages were inactivated by a wide range of wavelengths, suggesting photooxidative damage. Inactivation of fecal coliforms and somatic coliphages was mainly by shorter (UV-B) wavelengths, a result consistent with photobiological damage. Fecal coliform repair mechanisms appear to be activated in WSPs, and the surviving cells exhibit greater sunlight resistance in natural waters than those from raw sewage. In contrast, enterococci appear to suffer photooxidative damage in WSPs, rendering them susceptible to further photooxidative damage after discharge. This suggests that they are unsuitable as indicators of WSP effluent discharges to natural waters. Although somatic coliphages are more sunlight resistant than the other indicators in seawater, F-RNA phages are the most resistant in freshwater, where they may thus better represent enteric virus survival.

Sublethal effects of ultraviolet A radiation on Enterobacter cloacae

We report the sublethal effects of ultraviolet A (UVA) on Enterobacter cloacae in comparison with those produced in Escherichia coli. UVA-induced sublethal effects were investigated in either bacterial membrane and at tRNA level. Limited dependence on oxygen concentration for photoinduced inhibition of biochemical membrane functions and low levels of oxidative damage during the irradiation period were found in En. cloacae. On the other hand, ultraviolet spectroscopy and reversed-phase HPLC analysis of hydrolysed tRNA showed that radio induced damage to tRNA is similar in En. cloacae and E. coli. Nevertheless, growth delay induced by UVA in En. cloacae was shorter than that found in E. coli submitted to the same experimental conditions. A limited post-irradiation ppGpp accumulation and the absence of any influence of the membrane damage on the growth delay extent seem to be responsible for the shortness of this effect in En. cloacae. Most of the differences between En. cloacae and E. coli could be attributed to an increased ability of En. cloacae to overcome oxidative stress during UVA exposure.

Existing and potential applications of ultraviolet light in the food industry - a critical review

Short-wave ultraviolet light (UVC, 254 nm) can reduce dramatically the microbial load in air or on hard surfaces free from food residues, and can eliminate pathogens from potable water filtered to remove organic residues and 'clumps' of bacteria. More recently, approval of the Food and Drug Administration (USA) has been sought for a system for the destruction of pathogenic bacteria in fruit juices using UVC, and the same approach could perhaps be applied to remove spoilage organisms from cider or wines. In contrast, long-wave UV light (UVA, >320 nm) has limited microbiocidal properties, and for practical applications its effectiveness has to be enhanced by the presence of photosensitive compounds (eg furocoumarins) that will diffuse into a microbial cell prior to irradiation. The penetration of UVA into water is better than that of UVC, and its bacteriocidal action in the presence of photosensitisers can be rapid. However, pure furocoumarins are expensive and their addition to foodstuffs might be questioned on safety grounds. © 2000 Society of Chemical Industry.

Pseudomonas aeruginosa UV-A-induced lethal effect: influence of salts, nutritional stress and pyocyanine

The presence of NaCl in plating media shows an important protection against the Pseudomonas aeruginosa UV-A-induced lethal effect, contrasting with the known sensitizing action of salts on UV-A-irradiated Escherichia coli cells. MgSO4 exhibits a similar protection, but lower concentrations than for NaCl are needed to achieve the same effect. NaCl protection from lethal effects involves an osmotic mechanism, while MgSO4 could act by a different process. On the other hand, when cells grown in a complete medium are then incubated for 20 min in a synthetic medium and irradiated with UV-A, a very marked protection is obtained. This protection is dependent on protein synthesis, since treatment with tetracycline, during the nutritional stress, blocks its induction. These results offer a new example of cross-protection among different stressing agents. In our experimental conditions, natural phenazines of P. aeruginosa are not present in the cells, ruling out the possibility that these pigments act as photosensitizers. Conversely, pyocyanine (the major phenazine produced by this microorganism) prevents the UV-A killing effect in a concentration-dependent way when present in the irradiation media. Finally, UV-A irradiation induces, as in E. coli, the accumulation of guanosine tetraphosphate and guanosine pentaphosphate, although the physiological meaning of this finding has yet to be determined.

Inhibitory effect of solar radiation on thymidine and leucine incorporation by freshwater and marine bacterioplankton

We studied the effect of solar radiation on the incorporation of [(sup3)H]thymidine ([(sup3)H]TdR) and [(sup14)C]leucine ([(sup14)C]Leu) by bacterioplankton in a high mountain lake and the northern Adriatic Sea. After short-term exposure (3 to 4 h) of natural bacterial assemblages to sunlight just beneath the surface, the rates of incorporation of [(sup3)H]TdR and [(sup14)C]Leu were reduced at both sites by up to (symbl)70% compared to those for the dark control. Within the solar UV radiation (290 to 400 nm), the inhibition was caused exclusively by UV-A radiation (320 to 400 nm). However, photosynthetically active radiation (PAR) (400 to 700 nm) contributed almost equally to this effect. Experiments with samples from the high mountain lake showed that at a depth of 2.5 m, the inhibition was caused almost exclusively by UV-A radiation. At a depth of 8.5 m, where chlorophyll a concentrations were higher than those in the upper water column, the rates of incorporation of [(sup3)H]TdR were higher in those samples exposed to full sunlight or to UV-A plus PAR than in the dark control. In laboratory experiments with artificial UV light, the incorporation of [(sup3)H]TdR and [(sup14)C]Leu by mixed bacterial lake cultures was also inhibited mainly by UV-A. In contrast, in the presence of the green alga Chlamydomonas geitleri at a chlorophyll a concentration of 2.5 (mu)g liter(sup-1), inhibition by UV radiation was significantly reduced. These results suggest that there may be complex interactions among UV radiation, heterotrophic bacteria, and phytoplankton and their release of extracellular organic carbon. Our findings indicate that the wavelengths which caused the strongest inhibition of TdR and Leu incorporation by bacterioplankton in the water column were in the UV-A range. However, it may be premature to extrapolate this effect to estimates of bacterial production before more precise information on how solar radiation affects the transport of TdR and Leu into the cell is obtained.

Lethal effect induced in Pseudomonas aeruginosa Exposed to Ultraviolet-A radiation

Ultraviolet-A (365 nm, 120 kJ/m2/h) exposure caused cell death in Pseudomonas aeruginosa at doses at which Escherichia coli cell viability was not affected. We have not found that UVA induced growth delay or any other sublethal effect. Irradiated suspensions of P. aeruginosa showed a marked reduction in membrane-bound succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH) activities. Succinate-driven respiration and several nutrient transport systems were also inhibited. Whereas SDH and LDH activities were independent of the irradiation conditions, cell viability, respiration and transport systems were protected when irradiation was performed in an N2 atmosphere. A similar protective effect was observed when cells were grown in media containing glycerol or when preirradiation bacterial growth was carried out at 30 degrees C (instead of 37 degrees C). Results suggest that UVA induces a differential damaging effect on several biochemical functions of P. aeruginosa. The UVA- induced photodamage may fall into two categories: indirect damage mediated by oxygen (cell killing and inhibition of respiration and transport systems) and direct damage to SDH and LDH (apparently not oxygen dependent). These enzymes and leucine transport appear not to be involved in the lethal effect described herein because they were altered despite viability-preserving conditions

Evidence for UV-B-induced DNA degradation in Euglena gracilis mediated by activation of metal-dependent nucleases

It is demonstrated that in vivo irradiation with artificial UV-B for several hours significantly reduces the amount of large DNA extractable from immobilized Euglena in comparison with non-irradiated controls. This UV-B effect can be eliminated by a drastic reduction of the divalent ion concentration in the extracellular medium, i.e. the substitution of the culture medium by Tris-buffered agarose. Moreover, in vitro degradation of large DNA is demonstrated for crude protein extracts isolated from non-irradiated or UV-B-irradiated Euglena. The nuclease activity is shown for both crude protein extracts and purified nucleases; in both cases, two protein bands possessing nuclease activity are obtained with apparent molecular masses of 26 and 40 kDa and their activity is inhibited by specific nuclease inhibitors, i.e. aurintricarboxylic acid and ATP, applied at a concentration as low as 10(-8) M. Moreover, in vitro, nuclease activity clearly depends on the pH, with an optimum around pH 4.5, and on the ion composition of the extracellular medium. A strong stimulating effect is shown for Ca2+ with an optimum around 10(-4) M; this effect is potentiated by Zn2+ and Mn2+, but strongly counteracted by Mg2+ and the calmodulin inhibitors trifluoperazine and N- (6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W5). These results favour the concept which explains the lethal UV-B effect on Euglena as arising from a change in the general metabolic state of the cell and an activation of a DNA-degrading system, i.e. activation of metal-dependent nucleases (U.K. Tirlapur, D.-P. Häder and R. Scheuerlein, UV-B mediated damage in the photosynthetic flagellate, Euglena gracilis, studied by image analysis, Beitr. Biol. Pflanzen, 67 (1992) 305-317).

UV-A oxidative damage modified by environmental conditions in Escherichia coli

The effect of sublethal fluences (50-200 kJ m-2) of UV-A radiation (320-400 nm) in bacterial cells is a transient growth inhibition related to photo-modified tRNA and is associated with changes in membrane structure and function. Higher UV-A fluences result in cell death due to the production of reactive oxygen species, so far undetected at sublethal doses. Oxidative mechanisms of toxicity induced by 120 kJ m-2 UV-A radiation can be recorded by ultra-weak chemiluminescence, useful in quantifying oxidative reactions. When Escherichia coli was exposed to UV-A stress at a fluence rate equivalent to that of the Sun in the biosphere (33 W m-2), chemiluminescence levels were proportional to the photodamage. Chemiluminescence and photo-damage are linearly proportional and dependent on environmental conditions of the cells. It is postulated that in addition to tRNA photo-modification, UV-A alters the membrane structure of E. coli by oxidative damage, since changes in the membrane structure under different environmental conditions play a key role in the cell's response to UV-A injury.

Inactivation of enterococci and fecal coliforms from sewage and meatworks effluents in seawater chambers

Inactivation in sunlight of fecal coliforms (FC) and enterococci (Ent) from sewage and meatworks effluents was measured in 300-liter effluent-seawater mixtures (2% vol/vol) held in open-topped chambers. Dark inactivation rates (kDs) were measured (from log-linear survival curves) in enclosed chambers and 6-liter pots. The kD for FC was 2 to 4 times that for Ent, and inactivation was generally slower at lower temperatures. Sunlight inactivation was described in terms of shoulder size (n) and the slope (k) of the log-linear portion of the survival curve as a function of global solar insolation and UV-B fluence. The n values tended to be larger for Ent than for FC, and the k values for FC were around twice those for Ent in both effluent-seawater mixtures. The combined sunlight data showed a general inactivation rate (k) ranking in effluent-seawater mixtures of meatworks FC > sewage FC > meatworks Ent > sewage Ent. Describing 90% inactivation in terms of insolation (S90) gave far less seasonal variation than T90 (time-dependent) values. However, there were significant differences in inactivation rates between experiments, indicating the contribution to inactivation of factors other than insolation. Inactivation rates under different long-pass optical filters decreased with the increase in the spectral cutoff wavelength (lambda 50) of the filters and indicated little contribution by UV-B to total inactivation. Most inactivation appeared to be caused by two main regions of the solar spectrum--between 318 and 340 nm in the UV region and > 400 nm in the visible region.

Non-nuclear damage and cell lysis are induced by UVA, but not UVB or UVC, radiation in three strains of L5178Y cells

The potential to induce non-nuclear changes in mammalian cells has been examined for (1) UVA1 radiation (340-400 nm, UVASUN 2000 lamp), (2) UVA+UVB (peak at 313 nm) radiation (FS20 lamp), and (3) UVC (254 nm) radiation (G15T8 lamp). The effects of irradiation were monitored in vitro using three strains of L5178Y (LY) mouse lymphoma cells that markedly differ in sensitivity to UV radiation. Comparisons were made for the effects of approximately equitoxic fluences that reduced cell survival to 1-15%. Depending on the cell strain, the fluences ranged from 830 to 1600 kJ/m2 for the UVASUN lamp, 75 to 390 J/m2 for the FS20 lamp and 3.8 to 17.2 J/m2 for the G15T8 lamp. At the exposure level used in this study, irradiation with the UVASUN, but not the FS20 or G15T8, lamp induced a variety of non-nuclear changes including damage to cytoplasmic organelles and increased plasma membrane permeability and cell lysis. Cell lysis and membrane permeabilization were induced by the UVA1 emission of the UVASUN lamp, but not by its visible+IR components (> 400 nm). The results show that the plasma membrane and other organelles of LY cells are highly sensitive to UVA1 but not to UVB or UVC radiation. Also UVA1, but not UVB or UVC radiation, causes rapid and extensive lysis of LY cells. In conclusion, non-nuclear damage contributes substantially to UVA cytotoxicity in all three strains of LY cells.

An action spectrum for UV-induced attachment of V79 Chinese hamster cells to a substratum

When cells growing in monolayers are exposed to ultraviolet radiation (UV) their binding to the substratum is increased in strength. An action spectrum for such UV-induced binding was determined, using the time needed for trypsin-EDTA to detach the cells as a measure of the binding strength. This action spectrum was significantly different from the action spectrum for cell inactivation, which was also determined. At the shortest wavelengths (297/302, 313 nm) lethal fluences were needed to induce measurable binding while at the longest wavelengths (365, 405 nm) completely nonlethal fluences induced strong and persistent binding. Thus, different chromophores are involved in the two processes: while DNA may be the main chromophore for cell inactivation, other and unidentified chromophores may be more important for induction of increased cell binding to the substratum.

UVA-induced lipid peroxidation in cultured human fibroblasts

The UVA irradiation of cultured human fibroblasts leads to the formation and to the release of thiobarbituric acid-reactive substances in the supernatant. The major thiobarbituric acid-reactive substance is identified by fluorescence spectroscopy and HPLC, as malondialdehyde or malondialdehyde-forming substances under the thiobarbituric acid assay conditions. Malondialdehyde formation strongly suggests a UVA-induced lipid peroxidation. Lipid peroxidation is also supported by the inhibitory effect of D,L-alpha-tocopherol, the well-known chain breaking antioxidant, by the additional malondialdehyde formation in the dark after the photooxidative stress and by membrane damage revealed by lactate dehydrogenase leakage.

Hyperthermia potentiates the effects of aluminum phthalocyanine tetrasulfonate-mediated photodynamic toxicity in human malignant and normal cell lines

The purpose of this study was to examine the effects of photodynamic therapy utilizing aluminum phthalocyanine tetrasulfonate in vitro on several human malignant and normal cell types, with or without hyperthermia. Cells examined included normal skin fibroblasts, HT-1080 fibrosarcoma cells, SCC-25 (squamous cell carcinoma) and malignant melanoma cells. An argon-pumped continuous wave tunable dye laser at 675 nm was used as the light source, hyperthermia groups were heated to 42.5 degrees C, and radioisotope incorporation was used to measure DNA and protein synthesis as toxicity assays. Results showed an energy-dose, and A1PcS-concentration dependent toxicity in all cell lines examined, with moderate selectivity toward malignant cells. Hyperthermia alone was slightly toxic in melanomas and HT-1080 cell lines but had no effect in normal fibroblasts or SCC-25 cells. Hyperthermia synergistically potentiated the effects of PDT in all cell lines, and the combined modality was significantly more toxic in all malignant cell lines compared with normal cells. Thus, addition of hyperthermia to PDT protocols may enhance the efficacy of this treatment modality in vitro.

Growing Escherichia coli mutants deficient in riboflavin biosynthesis with non-limiting riboflavin results in sensitization to inactivation by broad-spectrum near-ultraviolet light (320-400 nm)

Two mutants of Escherichia coli unable to synthesize riboflavin were grown with limiting (2 micrograms ml-1) and non-limiting (10 micrograms ml-1) concentrations of riboflavin. These riboflavin auxotrophs when grown to exponential phase with non-limiting riboflavin are more sensitive to broad spectrum near-ultraviolet light (NUV, 320-400 nm) inactivation than when they are grown with limiting riboflavin. Exponential phase cells of the riboflavin auxotrophs grown with limiting riboflavin are sensitized when irradiated in saline supplemented with riboflavin. This suggests that extracellular riboflavin is important as a NUV sensitizer when intracellular levels of riboflavin are reduced. The concentration of riboflavin in crude extracts from exponentially growing cells correlates well with the sensitivity of these mutants to NUV inactivation. The level of riboflavin supplementation has little effect on the NUV sensitivity of the parental strain.

Role of cloned carotenoid genes expressed in Escherichia coli in protecting against inactivation by near-UV light and specific phototoxic molecules

Genes controlling carotenoid synthesis were cloned from Erwinia herbicola and expressed in an Escherichia coli strain. Carotenoids protect against high fluences of near-UV (NUV; 320 to 400 nm) but not against far-UV (200-300 nm). Protection of E. coli cells was not observed following treatment with either psoralen or 8-methoxypsoralen plus NUV. However, significant protection of cells producing carotenoids was observed with three photosensitizing molecules activated by NUV (alpha-terthienyl, harmine, and phenylheptatriyne) which are thought to have the membrane as an important lethal target. Protection of carotenoid-producing cells against inactivation was not observed with acridine orange plus visible light but was seen with toluidine blue O plus visible light.

Escherichia coli strains carrying the cloned cytochrome d terminal oxidase complex are sensitive to near-UV inactivation

To determine if membrane-bound cytochromes function as endogenous near-UV photosensitizers, strains containing the cloned cydA and cydB genes were tested for near-UV sensitivity. A strain containing both cloned genes overproduced cytochromes b558, b595, and d. Another strain containing only cloned cydB overproduced cytochrome b558. Both cytochrome-overproducing strains were hypersensitive to broad-spectrum near-UV inactivation. The presence of excess cytochromes did not affect sensitivity to far-UV radiation and provided protection against H2O2 inactivation.

Effect of growth temperature on lipid composition and ultraviolet sensitivity of human cells

Human skin fibroblasts were incubated at either 25 or 37 degrees C before UV irradiation. Cells incubated at 25 degrees C were more resistant to near UV radiation than cells grown at 37 degrees C, but cells grown at the lower temperature were more sensitive to 254 nm radiation. Fatty acid analysis of membranes of cells showed that cells incubated at the lower temperature contained significantly higher amounts of linoleic acid (18:2) and linolenic acid (18:3) than cells incubated at 37 degrees C. To determine if this difference in fatty acid content of the membranes was responsible for the UV survival characteristics of cells incubated at different temperatures, cells were enriched with either linoleate or linolenate during a 37 degrees C incubation period. Gas chromatography revealed that cells incorporated the supplied fatty acid. Fatty acid enriched cells were then irradiated with near UV, and survival characteristics were compared to those obtained with cells grown at the lower incubation temperature. The results suggest that the different proportion of fatty acid content of the cells is not the cause of different UV sensitivities of cells grown at 25 degrees C compared to cells grown at 37 degrees C.

Oxidative mechanisms of toxicity of low-intensity near-UV light in Salmonella typhimurium

The exposure of Salmonella typhimurium to environmentally relevant near-UV light stress has been studied by the use of a low-intensity, broad-band light source. The exposure of cells to such a light source rapidly induced a growth delay; after continuous exposure for 3 to 4 h, cells began to die at a rapid rate. The oxidative defense regulon controlled by the oxyR gene was involved in protecting cells from being killed by near-UV light. This killing may be potentiated by the overexpression of near-UV-absorbing proteins. These results are consistent with near-UV toxicity involving the absorption of light by endogenous photosensitizers, leading to the production of active oxygen species. We have shown, however, that one such species, H2O2, is not a major photoproduct involved in killing by near-UV light. Strains lacking alkyl hydroperoxide reductase were more sensitive to near-UV light, indicating that such hydroperoxides may be photoproducts. Near-UV exposure induced sensitivity to high salt levels, indicating that membranes may be a target of near-UV toxicity and a possible source of alkyl hydroperoxides. The demonstration of the inactivation of the heme-containing protein catalase indicates that direct destruction of UV-absorbing macromolecules could be another factor in near-UV toxicity. Cells which have been exposed to near-UV light for long, but sublethal, periods of time (up to 4 h) can recover and resume growth if the UV exposure is stopped but become progressively more sensitive to further stresses, such as H2O2. This result indicates that cells gradually accumulated damage during near-UV exposure until toxic levels were reached.

Photosensitized reactions of nucleic acids

The main effects of near-ultraviolet and visible light on cellular DNA are reviewed with emphasis on base lesions, oligonucleotide single-strand breaks and DNA-protein cross-links. Model system photosensitization reactions of DNA are also discussed. This includes photodynamic effects, menadione-mediated photooxidation, photoionization of antibiotics, the photochemistry of 5-halogenopyrimidines and urocanic acid.

Photosensitivity diseases related to interior lighting

The most frequently used source of indoor lighting is the fluorescent tube. Although there are major variations in phosphors, the majority of these lamps are safe, efficient, and economical illuminators. These fluorescent light sources are currently our primary source of visible light; however, they emit small amounts of ultraviolet A light (UVA) as well as a somewhat larger percentage of infrared radiation. Photosensitivity diseases have been reported in each of these three broad wavelength bands. Specific examples include heat urticaria from infrared exposure, contact photosensitivity of the phototoxic type following exposure to dyes and visible light, and two relatively rare but disabling conditions from ultraviolet A exposure--solar urticaria and contact photosensitivity of the photoallergic type (persistent light reaction). During the past five years, eight patients with photosensitivity induced by musk ambrette and UVA have been treated at Columbia-Presbyterian Medical Center; six of these have been severely disabled and satisfy the criteria for persistent light reactors. Fifteen patients with solar urticaria have also been observed. Ten of these had reactions in the UVA range. The clinical and laboratory findings of these two groups of patients were presented.

Relaxation of supercoiled plasmid DNA by oxidative stresses in Escherichia coli

The relaxation of plasmid DNA was observed after the visible light irradiation of Escherichia coli AB1157 harboring plasmid pBR322 or some other plasmids in the presence of a photosensitizing dye, such as toluidine blue or acridine orange, and molecular oxygen. Treatment of the cells with hydroperoxides, such as tert-butyl hydroperoxide, cumene hydroperoxide, and hydrogen peroxide, also caused the plasmid DNA relaxation in vivo. Relaxation was not observed in these treatments of purified pBR322 DNA in vitro. Plasmid DNA relaxation was also detected after near-UV irradiation. Far-UV irradiation did not induce such relaxation.

Sensitivity of Legionella pneumophila to sunlight in fresh and marine waters

Studies were carried out to assess the sunlight sensitivity of Legionella pneumophila suspended in fresh and marine waters. Comparison studies on sunlight sensitivity of lake water bacteria, Pseudomonas aeruginosa, Escherichia coli and Streptococcus faecalis, were also undertaken. The effects of full sunlight and polyacrylic-screened sunlight were monitored in the study. Results indicate that L. pneumophila cells are slightly more sensitive to sunlight in seawater than in fresh water. Enumeration of sunlight-stressed bacteria in fresh water was found to be dependent on the medium used, and the following order of sensitivity to sunlight, from least to most sensitive, was noted: natural lake water bacteria, L. pneumophila, P. aeruginosa, E. coli, and S. faecalis.

Gene responsible for protecting Escherichia coli from sodium dodecyl sulfate and toluidine blue plus light

Escherichia coli cells were killed by visible light irradiation in the presence of the photosensitizing dye, toluidine blue. Two uvrB mutant strains of E. coli K-12 (AB1885 and N3-1) were much more sensitive than the isogenic uvrA and uvrC strains to treatment with toluidine blue plus light, suggesting that the uvrB+ gene product was involved in repair of DNA damage induced by the treatment. The uvrB+ gene cloned in a high- or low-copy-number plasmid was transformed into the uvrB strain (AB1885). Although all the transformants showed the same resistance as its wild-type strain (AB1157) to UV irradiation, they were as sensitive as AB1885 was to treatment with toluidine blue plus light. The two uvrB strains were more sensitive to sodium dodecyl sulfate than the other strains, suggesting that these strains had a defect in the cell surface. A sodium dodecyl sulfate-resistant revertant obtained from AB1885 was more resistant than AB1885 was to treatment with toluidine blue plus light. The two uvrB strains (AB1885 and N3-1) appear to have a defective gene (tentatively called dvl) different from uvrB. Its map position was around 7 min on the E. coli map.