Photoreactivation of Escherichia coli after Low- or Medium-Pressure UV Disinfection Determined by an Endonuclease Sensitive Site Assay

Abstract

Photoreactivation of Escherichia coli after inactivation by a low-pressure (LP) UV lamp (254 nm), by a medium-pressure (MP) UV lamp (220 to 580 nm), or by a filtered medium-pressure (MPF) UV lamp (300 to 580 nm) was investigated. An endonuclease sensitive site (ESS) assay was used to determine the number of UV-induced pyrimidine dimers in the genomic DNA of E. coli, while a conventional cultivation assay was used to investigate the colony-forming ability (CFA) of E. coli. In photoreactivation experiments, more than 80% of the pyrimidine dimers induced by LP or MPF UV irradiation were repaired, while almost no repair of dimers was observed after MP UV exposure. The CFA ratios of E. coli recovered so that they were equivalent to 0.9-, 2.3-, and 1.7-log inactivation after 3-log inactivation by LP, MP, and MPF UV irradiation, respectively. Photorepair treatment of DNA in vitro suggested that among the MP UV emissions, wavelengths of 220 to 300 nm reduced the subsequent photorepair of ESS, possibly by causing a disorder in endogenous photolyase, an enzyme specific for photoreactivation. On the other hand, the MP UV irradiation at wavelengths between 300 and 580 nm was observed to play an important role in reducing the subsequent recovery of CFA by inducing damage other than damage to pyrimidine dimers. Therefore, it was found that inactivating light at a broad range of wavelengths effectively reduced subsequent photoreactivation, which could be an advantage that MP UV irradiation has over conventional LP UV irradiation.

Effects of UV Radiation on Photolyase and Implications with Regards to Photoreactivation following Low- and Medium-Pressure UV Disinfection

“…This study shows that the dimer repair rates of photolyase decreased when exposed to both LP and MP UV radiation in vitro, an observation that differs from results of Oguma et al (10), who did not detect any change in the activity of MP UV-exposed photolyase. This could be because of the higher dimer concentration in the substrate used in this study and the lack of interferences from other photoproducts, which allowed for more sensitive detection of photolyase activity.…”

Photoreactivation ofEscherichia coli andYersinia enterolytica after Irradiation with a 222 nm Excimer Lamp Compared to a 254 nm Low-pressure Mercury Lamp

“…Nevertheless, clues are given in some papers that deal with the photoreactivation after irradiation with lowand medium-pressure UV sources [14,15,25]. The general conclusion in these papers is that the survival ratio of the bacteria after photoreactivation following medium-pressure lamps is smaller than that of low-pressure lamps.…”

A comparison of DNA repair and survival of Escherichia coli O157:H7 following exposure to both low- and medium-pressure UV irradiation

“…To date, no studies have investigated DNA repair in E. coli O157:H7 following MP UV and only limited conflicting studies have evaluated repair following LP UV exposure in water (Tosa & Hirata 1999;Sommer et al 2000;Mofidi et al 2002). Recent studies performed using non-pathogenic E. coli have indicated differences in the repair following low doses of MP and LP UV irradiation (Oguma et al 2002;Zimmer & Slawson 2002). These studies showed that LP and MP UV demonstrated similar levels of inactivation, however, following MP UV exposure DNA repair was greatly reduced.…”