Oxygen and photoinactivation ofEscherichia coliin UVA and sunlight

Abstract

Aims: To establish the influence of oxygen on Escherichia coli before, during and after exposure to UVA or simulated sunlight. Methods and Results: Bacterial suspensions were exposed either to UVA or simulated sunlight. Conventional aerobic plate counts of illuminated cell suspensions were consistently lower than those obtained under conditions where reactive oxygen species (ROS) were neutralized, either (i) by the addition of the peroxide scavenger sodium pyruvate (0AE05% w/v) to the medium with subsequent incubation in an anaerobic jar or (ii) by culturing on a prereduced medium within an anaerobic cabinet, indicating that a substantial proportion of such cells are sublethally injured. While the presence of oxygen during the growth period resulted in a greater resistance of aerobically grown cells to simulated sunlight compared with their anaerobic counterparts, the extent of inactivation during illumination was directly related to the dissolved oxygen content of the water. Conclusions:The results show that, at each stage, oxygen has a marked influence on the observed colony count. Significance and Impact of the Study: Overall, the results indicate that future studies of bacteria exposed to UVA or sunlight should consider the effects of oxygen at every stage in the procedure, and especially during enumeration, where the inhibitory effects of ROS must be neutralized in order to obtain a valid count. An investigation of the effects of ROS neutralization on the counts of faecal bacteria under field conditions in natural waters is now required to establish the significance of these finding to solar water treatment.

Genetic and Physiological Effects of Noncoherent Visible Light Combined with Hydrogen Peroxide on Streptococcus mutans in Biofilm

“…Overall, our results are in agreement with those of Khaen-graeng and Reed (14), who suggested that the sublethal damage to bacterial cells caused by light leads to an ROS-sensitive state since it imposes an additional stress on the bacteria. Affecting bacteria in biofilm is one of the greatest challenges in the prevention and treatment of infectious diseases such as those associated with dental biofilm.…”

Sunlight inactivation of Campylobacter jejuni and Salmonella enterica, compared with Escherichia coli, in seawater and river water

“…For example, counts of sunlight damaged cells may increase if resuscitation steps, anaerobic incubation, or oxygen scavengers are used (Khaengraeng & Reed 2005), which may result in some flattening of sunlight inactivation curves.…”

Comparative effectiveness of solar disinfection using small-scale batch reactors with reflective, absorptive and transmissive rear surfaces

“…Recent research (Khaengraeng and Reed, 2005) has demonstrated that this may underestimate the number of viable bacteria due to respiratory self-destruction (Aldsworth et al, 1999), where the antioxidant defences of sub-lethally injured cells are overwhelmed by reactive oxygen species (ROS) formed as by-products of respiration (Bloomfield et al, 1998): such cells are able to multiply and form colonies only under ROSneutralised conditions, achieved by the addition of ROSscavengers such as sodium pyruvate, and by growth under anaerobic conditions.…”

“…As in earlier studies (e.g. Reed, 1997;Khaengraeng and Reed, 2005) sterile distilled water (pH 5.5-6.0) was then added to the commercial mineral water bottles (900 ml) and to the custommade solar disinfection reactors (1050 ml). A rinsed pellet of E. coli was then added to each experimental bottle at an initial suspension density of E10 6 CFU ml À1 measured by plate count, as described below, and representing a dilution of approximately 1000-fold compared to the original stationary phase overnight culture.…”