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

Bucheli‐Witschel, Margarete; Bassin, Claudio; Egli, Thomas

doi:10.1111/j.1365-2672.2010.04802.x

Cited by 34 publications

(50 citation statements)

References 46 publications

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“…Growth rates determined for this interval were the following: 1.0 h ¡1 for ancestral, 0.5 h ¡1 for control and 0.4 h ¡1 for the UV-adapted cells (Table 1). There are several studies showing that variations in the growth rate determine, at Error bars for survival data not visible were smaller than the symbol least partly, the survival after exposure to diVerent physical stresses like ionizing radiation provided in form of X-rays (Freedman and Bruce 1971), chlorine dioxide (Berg et al 1982), mild heat, and UV-A radiation (Berney et al 2006) and UV-C radiation (Bucheli-Witschel et al 2010). The second main growth parameter varying between the strains, the asymptote, giving the maximal cell density reached at the end of active growth, was about one order of magnitude higher for the ancestral and the control strain compared with the UV-adapted strain MW01 (Table 1).…”

Section: Resultsmentioning

confidence: 97%

Growth phase-dependent UV-C resistance of Bacillus subtilis: data from a short-term evolution experiment

et al. 2011

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After 700 generations of a short-term evolution experiment with Bacillus subtilis 168, two strains were isolated, the UV-adapted strain MW01 and the UV-unexposed control strain DE69, and chosen for UV-C radiation resistance studies with respect to growth phase. The ancestral strain from the evolution experiment was used as reference for comparative purposes. Cells of the UV-adapted strain showed signiWcant diVerences in their physiology (growth behavior, doubling time, cell density, and sporulation capacity) and were more resistant to UV in all monitored stages. These Wndings implicate the evolution to an increased UV radioresistance was not limited to a speciWc growth phase and led to reduced growth dynamics, compared with those obtained from the ancestral and the control strain.

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Section: Resultsmentioning

confidence: 97%

Growth phase-dependent UV-C resistance of Bacillus subtilis: data from a short-term evolution experiment

et al. 2011

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“…It is well known that stationary-phase cells of several bacterial species show enhanced UV-C resistance (2,4). Accordingly, Salmonella Typhimurium STCC 878 in mid-log phase was more UV susceptible than cells in the stationary phase, showing a shorter shoulder.…”

Section: Discussionmentioning

confidence: 99%

“…UV resistance may vary with the species (27) and even with the strain (44). In addition, it is also known that microbial factors, such as the growth phase (2), can determinate microbial UV resistance.…”

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confidence: 99%

Inactivation of Salmonella enterica by UV-C Light Alone and in Combination with Mild Temperatures

Gayán

Serrano

Raso

et al. 2012

Appl Environ Microbiol

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The aim of this investigation was to study the efficacy of the combined processes of UV light and mild temperatures for the inactivation of Salmonella enterica subsp. enterica and to explore the mechanism of inactivation. The doses to inactivate the 99.99% (4D) of the initial population ranged from 18.03 (Salmonella enterica serovar Typhimurium STCC 878) to 12.75 J ml ؊1 (Salmonella enterica serovar Enteritidis ATCC 13076). The pH and water activity of the treatment medium did not change the UV tolerance, but it decreased exponentially by increasing the absorption coefficient. An inactivating synergistic effect was observed by applying simultaneous UV light and heat treatment (UV-H). A less synergistic effect was observed by applying UV light first and heat subsequently. UV did not damage cell envelopes, but the number of injured cells was higher after a UV-H treatment than after heating. The synergistic effect observed by combining simultaneous UV and heat treatment opens the possibility to design combined treatments for pasteurization of liquid food with high UV absorptivity, such as fruit juices.

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“…Excited sensitizers transfer energy or electrons to other parts of the cell, causing damage, or to molecular oxygen, producing reactive oxygen species (ROS) that cause photooxidative damage (38). Depending on whether energy or electrons are transferred to molecular oxygen, ROS such as singlet oxygen, superoxide, hydrogen peroxide, and hydroxyl radicals are formed and can damage membrane lipids, proteins, enzymes, or nucleic acids (14,31,38,39,49).Previous research on bacterial photoinactivation mechanisms has focused on E. coli (5,13,15). Limited work has specifically explored the relative contributions of exogenous and endogenous indirect photoinactivation with E. coli (41).…”

mentioning

confidence: 99%

“…Previous research on bacterial photoinactivation mechanisms has focused on E. coli (5,13,15). Limited work has specifically explored the relative contributions of exogenous and endogenous indirect photoinactivation with E. coli (41).…”

mentioning

confidence: 99%

Mechanisms for Photoinactivation of Enterococcus faecalis in Seawater

Sassoubre

Nelson

Boehm

2012

Appl Environ Microbiol

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bField studies in fresh and marine waters consistently show diel fluctuations in concentrations of enterococci, indicators of water quality. We investigated sunlight inactivation of Enterococcus faecalis to gain insight into photoinactivation mechanisms and cellular responses to photostress. E. faecalis bacteria were exposed to natural sunlight in clear, filtered seawater under both oxic and anoxic conditions to test the relative importance of oxygen-mediated and non-oxygen-mediated photoinactivation mechanisms. Multiple methods were used to assess changes in bacterial concentration, including cultivation, quantitative PCR (qPCR), propidium monoazide (PMA)-qPCR, LIVE/DEAD staining using propidium iodide (PI), and cellular activity, including ATP concentrations and expression of the superoxide dismutase-encoding gene, sodA. Photoinactivation, based on numbers of cultivable cells, was faster in oxic than in anoxic microcosms exposed to sunlight, suggesting that oxygen-mediated photoinactivation dominated. There was little change in qPCR signal over the course of the experiment, demonstrating that the nucleic acid targets were not damaged to a significant extent. The PMA-qPCR signal was also fairly stable, consistent with the observation that the fraction of PI-permeable cells was constant. Thus, damage to the membrane was minimal. Microbial ATP concentrations decreased in all microcosms, particularly the sunlit oxic microcosms. The increase in relative expression of the sodA gene in the sunlit oxic microcosms suggests that cells were actively responding to oxidative stress. Dark repair was not observed. This research furthers our understanding of photoinactivation mechanisms and the conditions under which diel fluctuations in enterococci can be expected in natural and engineered systems. H ealth risks posed by exposure to polluted recreational waters are assessed using levels of the fecal indicator bacteria Enterococcus spp. and Escherichia coli. The concentrations of these bacteria, however, are known to be highly variable (6,7,59,60). Intensive field studies show that their concentrations fluctuate on diurnal timescales due to sunlight exposure; concentrations drop during sunlit hours and rise after the sun sets (8,21,50,60,61). While enterococcal photoinactivation is well documented, the mechanisms of inactivation are not well understood, limiting our ability to predict when the process will be important under the wide range of conditions that exist in natural and engineered systems.Bacterial photoinactivation is the result of direct and indirect damage caused by sunlight exposure. Direct damage occurs when photons are absorbed directly by cellular molecules, leading to changes in chemical bond structure. The most common example is UVB damage to DNA, resulting in pyrimidine dimers that prevent DNA replication (39, 47, 51). Indirect damage can occur when photons are absorbed by endogenous (intracellular) sensitizers, such as porphyrins and flavins, or exogenous (extracellular) sensitizers, such as humic compound...

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

Cited by 34 publications

References 46 publications

Growth phase-dependent UV-C resistance of Bacillus subtilis: data from a short-term evolution experiment

Growth phase-dependent UV-C resistance of Bacillus subtilis: data from a short-term evolution experiment

Inactivation of Salmonella enterica by UV-C Light Alone and in Combination with Mild Temperatures

Mechanisms for Photoinactivation of Enterococcus faecalis in Seawater

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