UV-C Resistance Research Articles

Previous stress exposures influence subsequent UV-C resistance of Salmonella enterica in coconut liquid endosperm

This study determined the effects of prior exposures to stresses commonly encountered by cells in food production and processing environments on the subsequent UV-C inactivation rates of Salmonella enterica in coconut liquid endosperm. Seven different strains of S. enterica were separately exposed to individual stresses such as gradual acidification (final pH 4.5), abrupt desiccation (aw 0.96), or heat stress at 40 °C for 24 h, after which the test strains were cocktailed and subjected to UV-C challenge. Cells were also exposed to all possible combinations of the individual stresses and thereafter subjected to UV-C challenge. Cells exposed to all individual and combinations of stresses exhibited 1st order, log-linear inactivation behavior (R2 0.903 to 0.998). Cells previously exposed to singular heat stress had the highest UV-C resistance (DUV-C 43.8 mJ/cm2), while cells exposed to all simultaneous pH, aw, and heat stresses had the least (DUV-C 22.5 mJ/cm2). Heterologous adaptive mechanisms were observed after S. enterica cells were exposed to acid, acid + desiccation, heat, and acid + heat, with individual heat stress exposure resulting in the significantly most UV-C resistant cells. Results obtained in this study provide baseline information on the selection of appropriate challenge organism for establishment of UV-C process schedule for coconut liquid endosperm and similar commodities.

UV-C Adaptation of Shigella: Morphological, Outer Membrane Proteins, Secreted Proteins, and Lipopolysaccharides Effects.

Water UV disinfection remains extremely important, particularly in developing countries where drinking and reclaimed crop irrigation water may spread devastating infectious diseases. Enteric bacterial pathogens, among which Shigella, are possible contaminants of drinking and bathing water and foods. To study the effect of UV light on Shigella, four strains were exposed to different doses in a laboratory-made irradiation device, given that the ultraviolet radiation degree of inactivation is directly related to the UV dose applied to water. Our results showed that the UV-C rays are effective against all the tested Shigella strains. However, UV-C doses appeared as determinant factors for Shigella eradication. On the other hand, Shigella-survived strains changed their outer membrane protein profiles, secreted proteins, and lipopolysaccharides. Also, as shown by electron microscopy transmission, morphological alterations were manifested by an internal cytoplasm disorganized and membrane envelope breaks. Taken together, the focus of interest of our study is to know the adaptive mechanism of UV-C resistance of Shigella strains.

Deinococcus rubrus sp. nov., a Bacterium Isolated from Antarctic Coastal Sea Water.

Two Gram-staining-negative, red-pinkish, coccus-shaped, non-motile, and aerobic bacterial strains, designated Ant21T and Ant22, were isolated from the Antarctic coastal sea water. Strains Ant21T and Ant22 showed UVC and gamma radiation resistance. Phylogenetic analyses based on 16S rRNA gene sequences determined that these strains belong to the genus Deinococcus. Through the analyses of the 16S rRNA gene sequences, strains Ant21T and Ant22 were found to have 97.7% and 97.8% similarity to Deinococcus marmoris DSM 12784T and 97.0% and 97.2% similarity to Deinococcus saxicola AA-1444T, respectively. The sequence similarity with the type strains of other Deinococcus species was less than 96.9% for both strains. Strains Ant21T and Ant22 shared relatively high 16S rRNA gene sequence similarity (99.3%) and had a closely related DNA reassociation value of 84 ± 0.5%. Meanwhile, they showed a low level of DNA-DNA hybridization (<30%) with other closely related species of the genus Deinococcus. The two strains also showed typical chemotaxonomic features for the genus Deinococcus, in terms of the major polar lipid (phosphoglycolipid) and the major fatty acids (C16:0, C16:1ω6c/ω7c, iso-C17:0 , and iso-C15:0). They grew at temperatures between 4°C and 30°C and at pH values of 6.0-8.0. Based on the physiological characteristics, the 16S rRNA gene sequence analysis results, and the low DNA-DNA reassociation level with Deionococcus marmoris, strains Ant21T (= KEMB 9004-167T =JCM 31436T) and Ant22 (KEMB 9004-168 =JCM 31437) represent novel species belonging to the genus Deinococcus, for which the name Deinococcus rubrus is proposed.

Inactivation behaviors of selected bacteria in ultraviolet-C-treated human breast milk

Abstract This study determined the inactivation behaviors, which include inactivation pattern, sublethal injury development, and inactivation kinetic parameters of selected bacteria in UV-C treated human breast milk. Multi strain mixtures of Salmonella enterica, Escherichia coli O157:H7, non-pathogenic E. coli , Pseudomonas aeruginosa , Listeria monocytogenes, and a lone strain of Staphylococcus aureus were inoculated into donated breast milk prior to UV-C inactivation studies. Results showed that the test organisms exhibited two types of inactivation patterns, making it difficult to directly compare UV-C resistance. S. enterica and non-pathogenic E. coli exhibited a monophasic log-linear inactivation pattern within the 60-min UV-C treatment period. All other challenge organisms exhibited a biphasic inactivation pattern characterized by a faster initial log linear inactivation, followed by a slower inactivation tailing. Sublethal injury rates were small in all test organisms except for S. aureus , which developed total sublethal injury throughout the UV-C exposure. Despite the injury rates, S. aureus had the least total population reduction (2.63 log CFU) after the 60-min treatment, while S. enterica had the greatest reduction (3.88 log CFU). The inactivation behaviors established in this work provide baseline information in the development of a UV-C pasteurization equipment and process for breast milk.

The S-layer Protein DR_2577 Binds Deinoxanthin and under Desiccation Conditions Protects against UV-Radiation in Deinococcus radiodurans.

Deinococcus radiodurans has the puzzling ability to withstand over a broad range of extreme conditions including high doses of ultraviolet radiation and deep desiccation. This bacterium is surrounded by a surface layer (S-layer) built of a regular repetition of several proteins, assembled to form a paracrystalline structure. Here we report that the deletion of a main constituent of this S-layer, the gene DR_2577, causes a decrease in the UVC resistance, especially in desiccated cells. Moreover, we show that the DR_2577 protein binds the carotenoid deinoxanthin, a strong protective antioxidant specific of this bacterium. A further spectroscopical characterization of the deinoxanthin-DR_2577 complex revealed features which could suggest a protective role of DR_2577. We propose that, especially under desiccation, the S-layer shields the bacterium from incident ultraviolet light and could behave as a first lane of defense against UV radiation.

Deinococcus actinosclerus sp. nov., a novel bacterium isolated from soil of a rocky hillside.

Three Gram-stain-positive, catalase- and oxidase-positive coccus- or rod-shaped bacterial strains, designated BM2T, BM4 and BM5, were isolated from soil in South Korea. They showed strong resistance to gamma radiation with a D10 value of 9 kGy but weak UVC resistance. The 16S rRNA sequences of strains BM2T, BM4 and BM5 represent a novel subline within the genus Deinococcus in the family Deinococcaceae. The 16S rRNA gene sequences of strains BM2T, BM4 and BM5 were indistinguishable and showed 98.1-87.3 % similarity with other species of the genus Deinococcus. Strain BM2T exhibited relatively high levels of DNA-DNA hybridization with BM4 (87 ± 0.8 %) and BM5 (92 ± 1.2 %). Meanwhile, it showed a low level of DNA-DNA hybridization ( < 30 %) with other closely related species of the genus Deinococcus. The strains showed the typical chemotaxonomic characteristics of the genus Deinococcus, with the presence of menaquinone 8 as the respiratory quinone; the major fatty acids were summed feature 3 (composed of C16 : 1ω7c/C16 : 1ω6c), C15 : 1ω6c and C16 : 0. The DNA G+C content of strain BM2T was 69.7 mol%. The polar lipid profile included major amounts of phosphatidylglycerol, phosphatidylcholine and an unknown aminolipid. On the basis of phenotypic and genotypic properties, and phylogenetic distinctiveness, strains BM2T, BM4 and BM5 should be classified in a novel species in the genus Deinococcus, for which the name Deinococcus actinosclerus sp. nov. is proposed. The type strain is BM2T ( = KEMB 5401-184T = JCM 30700T); reference strains are BM4 ( = JCM 30701) and BM5 ( = JCM 30702).

Environmental and biological factors influencing the UV-C resistance of Listeria monocytogenes

In this investigation, the effect of microbiological factors (strain, growth phase, exposition to sublethal stresses, and photorepair ability), treatment medium characteristics (pH, water activity, and absorption coefficient), and processing parameters (dose and temperature) on the UV resistance of Listeria monocytogenes was studied. The dose to inactivate 99.99% of the initial population of the five strains tested ranged from 21.84 J/mL (STCC 5672) to 14.66 J/mL (STCC 4031). The UV inactivation of the most resistant strain did not change in different growth phases and after exposure to sublethal heat, acid, basic, and oxidative shocks. The pH and water activity of the treatment medium did not affect the UV resistance of L. monocytogenes, whereas the inactivation rate decreased exponentially with the absorption coefficient. The lethal effect of UV radiation increased synergistically with temperature between 50 and 60 °C (UV-H treatment). A UV-H treatment of 27.10 J/mL at 55 °C reached 2.99 and 3.69 Log10 inactivation cycles of L. monocytogenes in orange juice and vegetable broth, and more than 5 Log10 cycles in apple juice and chicken broth. This synergistic effect opens the possibility to design UV combined processes for the pasteurization of liquid foods with high absorptivity.

Resistance of Staphylococcus aureus to UV-C light and combined UV-heat treatments at mild temperatures

In this investigation, the resistance of enterotoxigenic Staphylococcus aureus to short-wave ultraviolet light (UV-C) and to combined UV C-heat (UV-H) treatments in buffers and in liquid foods with different physicochemical characteristics was studied. Microbial resistance to UV-C varied slightly among the S. aureus strains tested. The UV-C resistance of S. aureus increased in the entry of stationary growth phase, which in part was due to the expression of the alternative sigma factor σB. The UV-C resistance of S. aureus was independent of the treatment medium's pH and water activity, but it decreased exponentially as the absorption coefficient increased. UV-C bactericidal efficacy in liquids of high absorption coefficients was improved synergistically when combined with a mild heat treatment at temperatures ranging from 50.0 to 57.5°C. pH of the treatment medium modified the lethality of UV-H treatments and therefore the temperature of maximum synergy. The advantage of combined UV-H treatments was demonstrated in fruit juices and vegetable and chicken broths, inactivating 5 Log10 cycles of S. aureus by applying UV-C treatments of 27.1mJ/L for 3.6min at 52.5°C or 13.6mJ/L for1.8min at 55.0°C.

Targeted Gene Therapy of Xeroderma Pigmentosum Cells Using Meganuclease and TALEN™

Xeroderma pigmentosum group C (XP-C) is a rare human syndrome characterized by hypersensitivity to UV light and a dramatic predisposition to skin neoplasms. XP-C cells are deficient in the nucleotide excision repair (NER) pathway, a complex process involved in the recognition and removal of DNA lesions. Several XPC mutations have been described, including a founder mutation in North African patients involving the deletion of a TG dinucleotide (ΔTG) located in the middle of exon 9. This deletion leads to the expression of an inactive truncated XPC protein, normally involved in the first step of NER. New approaches used for gene correction are based on the ability of engineered nucleases such as Meganucleases, Zinc-Finger nucleases or TALE nucleases to accurately generate a double strand break at a specific locus and promote correction by homologous recombination through the insertion of an exogenous DNA repair matrix. Here, we describe the targeted correction of the ΔTG mutation in XP-C cells using engineered meganuclease and TALEN™. The methylated status of the XPC locus, known to inhibit both of these nuclease activities, led us to adapt our experimental design to optimize their in vivo efficacies. We show that demethylating treatment as well as the use of TALEN™ insensitive to CpG methylation enable successful correction of the ΔTG mutation. Such genetic correction leads to re-expression of the full-length XPC protein and to the recovery of NER capacity, attested by UV-C resistance of the corrected cells. Overall, we demonstrate that nuclease-based targeted approaches offer reliable and efficient strategies for gene correction.

Endurance of the endolithic desert cyanobacterium Chroococcidiopsis under UVC radiation

Desert cyanobacteria of the genus Chroococcidiopsis are extremely resistant to desiccation and ionizing radiation. When an endolithic strain was exposed to UVC radiation cell lysis, genome damage, photosynthetic pigment bleaching and reduced photochemical performance occurred. Nevertheless, survivors were scored after UVC doses as high as 13kJ/m(2) and their endurance ascribed to multicellular aggregates enveloped in thick envelopes, so that attenuated UVC radiation reached the inner cells. In addition, the accumulation of carotenoids contributed to UVC resistance by providing protection against oxidative stress. Finally, in survivors repair mechanisms were responsible for the recovery of the induced damage to genome and photosynthetic apparatus.

UV-C Inactivation ofCronobacter sakazakii

The purpose of this research was to study the effect of different factors on the resistance of Cronobacter sakazakii NCTC 9238 to UV-C light (which includes germicidal ultraviolet light at 254 nm) and to determine whether a combined treatment with heat would produce a synergistic effect for its inactivation. Growth temperature between 10°C and 37°C did not change the UV-C resistance of C. sakazakii. On the contrary, cells in the logarithmic phase of growth were more sensitive to UV-C light than in the stationary phase. The lethality of UV-C was independent of pH (between 3.0 and 7.0) and a(w) (between 0.94 and > 0.99) of the treatment media, but it exponentially decreased with the absorption coefficient (α). When applying a UV-C treatment of 27.1 J/mL at 25°C to C. sakazakii suspended in vegetable soup and apple juice, 1 and 2 log10 cycles of inactivation were barely achieved, respectively. However, the bactericidal effect of UV-C light increased with temperature. The lethality of the combined process was the result of a synergistic effect that was maximum at 52.5°C for apple juice and 55°C for vegetable soup. In conclusion, these results indicate that UV-C efficacy may be influenced by microbial growth conditions and food characteristics, and that its combination with heat may act synergistically against C. sakazakii.

Survival ofBacillus pumilusSpores for a Prolonged Period of Time in Real Space Conditions

To prevent forward contamination and maintain the scientific integrity of future life-detection missions, it is important to characterize and attempt to eliminate terrestrial microorganisms associated with exploratory spacecraft and landing vehicles. Among the organisms isolated from spacecraft-associated surfaces, spores of Bacillus pumilus SAFR-032 exhibited unusually high resistance to decontamination techniques such as UV radiation and peroxide treatment. Subsequently, B. pumilus SAFR-032 was flown to the International Space Station (ISS) and exposed to a variety of space conditions via the European Technology Exposure Facility (EuTEF). After 18 months of exposure in the EXPOSE facility of the European Space Agency (ESA) on EuTEF under dark space conditions, SAFR-032 spores showed 10-40% survivability, whereas a survival rate of 85-100% was observed when these spores were kept aboard the ISS under dark simulated martian atmospheric conditions. In contrast, when UV (>110 nm) was applied on SAFR-032 spores for the same time period and under the same conditions used in EXPOSE, a ∼7-log reduction in viability was observed. A parallel experiment was conducted on Earth with identical samples under simulated space conditions. Spores exposed to ground simulations showed less of a reduction in viability when compared with the "real space" exposed spores (∼3-log reduction in viability for "UV-Mars," and ∼4-log reduction in viability for "UV-Space"). A comparative proteomics analysis indicated that proteins conferring resistant traits (superoxide dismutase) were present in higher concentration in space-exposed spores when compared to controls. Also, the first-generation cells and spores derived from space-exposed samples exhibited elevated UVC resistance when compared with their ground control counterparts. The data generated are important for calculating the probability and mechanisms of microbial survival in space conditions and assessing microbial contaminants as risks for forward contamination and in situ life detection.

UV-C inactivation of Escherichia coli at different temperatures

The influence of treatment parameters (dose and temperature), treatment medium characteristics (absorption coefficient, pH and water activity) and microbiological factors (strain, growth phase and UV damage and repair capacity) on Escherichia coli UV-C resistance has been investigated. UV-C doses to inactivate at 25 °C 99.99% of the initial population (4D) of five strains of E. coli in McIlvaine buffer of pH 7.0 with tartrazine added (absorption coefficient of 10.77 cm−1) were 16.60, 14.36, 14.36, 13.22, 11.18 J/mL for strains E. coli STCC 4201, STCC 471, STCC 27325, O157:H7 and ATCC 25922, respectively. The entrance in the stationary growth phase increased the 4D value of the most resistant strain, E. coli STCC 4201, from 13.09 to 17.23 J/mL. Survivors to UV treatments showed neither oxidative damages nor injuries in cell envelopes. On the contrary, the photoreactivation by the incubation of plates for 60 min below visible light (11.15 klx) increased the dose to 18.97 J/mL. The pH and the water activity of the treatment medium did not affect the UV tolerance of E. coli STCC 4201, but the lethal effect of the treatments decreased exponentially (Log10 4D = − 0.0628α + 0.624) by increasing the absorption coefficient (α). A treatment of 16.94 J/mL reached 6.35, 4.35, 2.64, 1.93, 1.63, 1.20, 1.02 and 0.74 Log10 cycles of inactivation with absorption coefficients of 8.56, 10.77, 12.88, 14.80, 17.12, 18.51, 20.81 and 22.28 cm−1. The temperature barely changed the UV resistance up to 50.0 °C. Above this threshold, inactivation rates due to the combined process synergistically increased with the temperature. The magnitude of the synergism decreased over 57.5 °C. An UV treatment of 16.94 J/mL in media with an absorption coefficient of 22.28 cm−1 reached 1.23, 1.64, 2.36, 4.01 and 6.22 Log10 cycles of inactivation of E. coli STCC 4201 at 50.0, 52.5, 55.5, 57.5 and 60.0 °C, respectively. Results obtained in this investigation show that UV light applied at mild temperatures (57.5 to 60 °C) could be an alternative to heat treatments for 5-Log10 reductions of E. coli in liquid foods. Since microbial resistance to UV-C light did not depend on the pH and water activity (aw) of the treatment media, eventual advantages of UV light for pasteurization purposes will be higher in low aw foods. E. coli STCC 4201 could be considered as a target when UV light processing of foods.

UV-C inactivation in Escherichia coli is affected by growth conditions preceding irradiation, in particular by the specific growth rate

The objective was to analyse the impact of growth conditions, in particular of the specific growth rate, on the resistance of Escherichia coli towards UV-C irradiation. Escherichia coli K12 wild-type bacteria (and in some experiments also a mutant not expressing RpoS, the global regulator of the general stress response; rpoS(-) mutant) were cultivated either in batch culture until stationary phase was reached or in continuous culture at different specific growth rates (μ) and then irradiated with UV-C light. Inactivation was determined by plating. The specific growth rate had a profound effect on UV-C resistance. Stationary phase or very slowly growing cells (0≤μ<0·1 h(-1)) as well as fast-growing cells exhibited a high resistance compared to bacteria growing at an intermediate rate (between 0·2 and 0·4 h(-1) ). The rpoS(-) mutant was more susceptible to UV irradiation than the wild-type when obtained from stationary phase, while mutant cells from continuous culture (μ=0·2 h(-1)) revealed a UV-C resistance similar to the wild-type grown under the same conditions. Antecedent growth conditions determine the physiological state of bacteria including the resistance towards UV-C irradiation. In particular, the specific growth rate was shown to markedly affect UV-C resistance of E. coli. The observed pattern of UV-C resistance exhibiting a minimum at intermediate specific growth rates must be explained by two or several counteracting mechanisms. For lower specific growth rates, the regulator of the global stress response, RpoS, is at least partly involved in the physiological processes responsible for UV-C resistance. The observed impact of antecedent growth conditions on UV-C resistance of E. coli stresses the necessity to use clearly defined cultivation conditions and to report them to gather meaningful and comparable data on the UV-C resistance of micro-organisms.

Involvement of recF in 254 nm Ultraviolet Radiation Resistance in Deinococcus radiodurans and Escherichia coli

recF is a critical gene involved in the RecFOR pathway of DNA repair in Deinococcus radiodurans (D. radiodurans). To investigate the role of recF in UV-C radiation resistance, we generated the recF-deficient D. radiodurans strain R1, expressed recF in Escherichia coli (E. coli) BL21 cells, and compared the ability of each to resist UV-C radiation by F (10), inactivation constant (IC), and extrapolation number (N). The mutation of recF in D. radiodurans R1 resulted in characteristic slow growth and dramatic sensitivity to UV-C irradiation. Transformation of recF into E. coli BL21 cells resulted in increased UV-C resistance compared to untransformed E. coli BL21 cells. These results suggested that recF is needed for the replication of D. radiodurans. Furthermore, as a part of the RecFOR pathway in D. radiodurans, disruption of recF could dramatically decrease the UV-C resistance of D. radiodurans and recF could increase the UV-C resistance of E. coli BL21 cells.

Complete genome sequence of Geodermatophilus obscurus type strain (G-20).

Geodermatophilus obscurus Luedemann 1968 is the type species of the genus, which is the type genus of the family Geodermatophilaceae. G. obscurus is of interest as it has frequently been isolated from stressful environments such as rock varnish in deserts, and as it exhibits interesting phenotypes such as lytic capability of yeast cell walls, UV-C resistance, strong production of extracellular functional amyloid (FuBA) and manganese oxidation. This is the first completed genome sequence of the family Geodermatophilaceae. The 5,322,497 bp long genome with its 5,161 protein-coding and 58 RNA genes is part of the Genomic Encyclopedia of Bacteria and Archaea project.

Annexin II is involved in UVC resistance of human cells and HSP27 which regulates the metabolism of annexin II

Annexin II is involved in UVC resistance of human cells and HSP27 which regulates the metabolism of annexin II

When Does Subjective Day Come Under 24-h Light/Dark Cycles?: The Case of Circadian Rhythms of UV-C Resistance and Timing of Cell Division in Euglena gracilis

When Does Subjective Day Come Under 24-h Light/Dark Cycles?: The Case of Circadian Rhythms of UV-C Resistance and Timing of Cell Division in Euglena gracilis

Effects of forespore-specific overexpression of apurinic/apyrimidinic endonuclease Nfo on the DNA-damage resistance properties of Bacillus subtilis spores

The effects of overexpression of the apurinic/apyrimidinic DNA endonuclease Nfo on wet and dry heat and UV-C (254 nm) resistance of Bacillus subtilis spores with or without alpha/beta-type small, acid-soluble spore proteins (SASP) were determined. Results revealed that overexpression of Nfo > or =50-fold in spores increased the wet heat resistance of exoA nfo B. subtilis spores (termed alpha(-)beta(-)) that lack most alpha/beta-type SASP, but had no effect on these spores' UV-C resistance. Nfo overexpression also increased these spores' dry heat resistance, and to levels slightly greater than that of wild-type spores. These results are consistent: (1) with wet and dry heat (but not UV-C) generating abasic sites in alpha(-)beta(-) spore DNA; (2) with dry heat generating some of these lesions in spores that retain alpha/beta-type SASP; and (3) indicate that Nfo can repair these abasic lesions following spore germination.

Annexin II, a Novel HSP27‐interacted Protein, is Involved in Resistance to UVC‐induced Cell Death in Human APr‐1 Cells

Heat shock protein 27 (HSP27) is implicated in diverse biologic functions as a molecular chaperone. We found that HSP27 is involved in the protection of human cells against UVC lethality. To elucidate the molecular mechanisms underlying UVC resistance, we searched for HSP27-interacted proteins related to resistance in UVC-resistant human cells, APr-1. Three candidates for HSP27-interacted proteins were found from cell lysates using an affinity column coupled with GST-fused HSP27 protein. Interaction between HSP27 and two candidates, annexin II and HSP70, was confirmed by immunoprecipitation analysis. After UVC irradiation, the amount of the complex of HSP27 and annexin II decreased in the postnuclear fraction, while it increased in the nuclear fraction. Cells transfected with annexin II-siRNA were more susceptible to UVC lethality. These results suggest that annexin II is a novel HSP27-interacted protein which is involved in UVC resistance in human cells, at least those tested here.