Indicators for photoreactivation and dark repair studies following ultraviolet disinfection

Abstract

Repair of DNA in bacteria following ultraviolet (UV) disinfection can cause reactivation of inactivated bacteria and negatively impact the efficiency of the UV disinfection process. In this study, various strains of E. coli (wild-type, UV-resistant and antibiotic-resistant strains) were investigated for their ability to perform dark repair and photoreactivation, and compared based on final repair levels after 4 h of incubation, as well as repair rates. Analysis of the results revealed that the repair abilities of different E. coli strains can differ quite significantly. In photoreactivation, the log repair ranged from 10 to 85%, with slightly lower log repair percentages when medium-pressure (MP) UV disinfection was employed. In dark repair, log repair ranged from 13 to 28% following low-pressure (LP) UV disinfection. E. coli strains ATCC 15597 and ATCC 11229 were found to repair the fastest and to the highest levels for photoreactivation and dark repair, respectively. These strains were also confirmed to repair to higher levels when compared to a pathogenic E. coli O157:H7 strain. Hence, these strains could possibly serve as conservative indicators for future repair studies following UV disinfection. In addition, dimer repair by photoreactivation and dark repair was also confirmed on a molecular level using the endonuclease sensitive site (ESS) assay.

Inactivation and Photorepair of Enteric Pathogenic Microorganisms with Ultraviolet Irradiation

“…Traditional water disinfection processes rely heavily on chemical disinfectants, such as chlorine, which produce chemical disinfection by-products in finished drinking water (Muellner et al, 2007). Because it does not produce chemical disinfection by-products and has excellent biocidal properties, ultraviolet (UV) disinfection is now highly regarded as an alternative to chlorination for the treatment of drinking water (Quek and Hu, 2008;Wolfe, 1990). However, because UV radiation from the sun is present in the environment, natural defense mechanisms have evolved in bacteria and other microorganisms that allow UVinactivated microorganisms to reverse UV-induced damage through such repair pathways as photoreactivation and dark repair (Koivunen and Heinonen-Tanski, 2005;Quek and Hu, 2008).…”

Solar disinfection modeling and post-irradiation response of Escherichia coli in wastewater

“…From the observations above, it can be concluded that the constant supply of light leads to adaptation of the population on the stress conditions, also verified by Berney et al [38] and therefore the phenomenon of persistence as suggested by Giacobone and Opezzo [39] can explain these findings. The new generations of bacteria that derive from stressed ones are more prone to survive the light impact [41] and even adapt better to a new stress [29]. It should also be noted here that the non-lethal light also provides the opportunity for excess growth, due to the nutrients present in the matrix.…”

Elucidating bacterial regrowth: Effect of disinfection conditions in dark storage of solar treated secondary effluent

“…However, prolonging their treatment in this favorable temperature promotes multiplication and therefore, new strains, that gain resistance against solar irradiation in conditions of exposure to (visible) light [13,23,37]. This bacterial ability is a heritage of evolution through time, to protect themselves from the natural ultraviolet rays from the sun [27].…”