Visible light damage to Escherichia coli in seawater: oxidative stress hypothesis

Abstract

The effect of visible light on Escherichia coli H10407 in seawater microcosms was investigated. Light damage was estimated by loss of colony-forming ability. Illumination of E. coli suspended in oligotrophic seawater with visible light at an intensity of about 40 klux caused a drastic decrease of culturable bacteria which turned to a viable but non-culturable state. In seawater E. coli exhibited weak metabolic activity as estimated by 3H methyl-thymidine incorporation in the cell. Visible light did not significantly alter this metabolic activity and did not involve detectable oxidation of lipid membranes as evaluated by gas chromatography analysis of fatty acids. The involvement of oxygen and reactive oxygen species in phototoxicity was studied. A decrease of the toxic effect was observed when E. coli was exposed to visible light under anaerobic conditions. Scavengers of reactive oxygen species exhibited variable protective effects. beta-Carotene, a singlet oxygen scavenger, and superoxide dismutase were equally ineffective. On the other hand, catalase, which eliminates hydrogen peroxide and thiourea, a hydroxyl radical scavenger, showed a net protection. In addition desferrioxamine B, an iron chelator, was also effective in reducing phototoxicity, probably by preventing hydroxyl radical generation by decomposition of hydrogen peroxide in the presence of iron (Fenton reaction). Therefore, hydrogen peroxide and hydroxyl radical seem to be reactive intermediates of oxygen-dependent (type II) photosensitized reactions.

Environmental and physico-chemical factors induce VBNC state in Listeria monocytogenes

“…The most harmful effect was found when bacteria behavior was analyzed according to the culturability pattern. The effect of sunlight on culturability has been reported by numerous authors in both fresh water and seawater [16]. Barcina et al [1] concluded that one of the effects of visible radiation on Escherichia coli cells in fresh water is the progressive loss of their capacity to multiply in standard bacteriological media.…”

“…A number of factors induce the VBNC state, including starvation, which is probably the most predominant factor for most of the bacteria studied [15,20,28,33], temperature [32], NaCl concentration [30,33] and visible light [8,16]. The conditions shown to induce nonculturability differ according to the organism [24].…”

Microbiology and atmospheric processes: chemical interactions of primary biological aerosols

“…Cells have at their disposition enzymes (superoxidase, peroxydases etc.) which reduce or trap radicals such as β-carotene (Gourmelon et al, 1994;Ochsner et al, 2000). When nutrient concentrations (organic matter essentially) are not sufficient, the global cell metabolism can be reduced and cell development can be stopped.…”

Zinc enhances the phototoxic effect of blue light against malodour-producing bacteria in an experimental oral biofilm

“…photodynamic treatment) has been reported in the literature (Wilson, 1994;Henry et al, 1995Henry et al, , 1996Konig et al, 2000;Soukos et al, 2005), and it has been suggested that this effect is mediated through the production of ROS (Gourmelon et al, 1994). This hypothesis is further supported by the observation that obligate anaerobic oral bacteria (pigmented and non-pigmented) are more susceptible to blue light exposure treatment than facultative ones (Feuerstein et al, 2004;Sterer & Feuerstein, 2005).…”

“…It was further suggested that light-induced production of reactive oxygen species (ROS) is the mechanism underlying this phototoxic effect (Gourmelon et al, 1994). The aim of the present study was to test the hypothesis that zinc may promote the phototoxic effect of high-intensity blue light against malodour-producing bacteria in an experimental model of oral biofilm.…”