Determination of pyrimidine dimers in the genomic DNA of Escherichia coli during photoreactivation following inactivation by medium-pressure UV lamp
A polychromatic medium-pressure (MP) UV lamp was compared with a monochromatic low-pressure (LP) UV lamp to investigate the inactivation and the subsequent photoreactivation of Escherichia coli . An endonuclease sensitive site (ESS) assay was applied to determine the number of UV-induced pyrimidine dimers in the genomic DNA of E.coli in parallel with a conventional colony forming assay. more than 95% of the ESS in the DNA of E.coli was repaired in both cases while the colony forming ability ratio of E.coli recovered to be equivalent to 0.8log or 1.2log inactivation, respectively. After a 3log inactivation by the LPUV lamp, more than 90% of the ESS was repaired and the colony forming ability ratio recovered to the equivalent of 1.2log inactivation. After a 3log inactivation by the MPUV lamp, almost no ESS was repaired and the colony forming ability ratio showed little recovery to the equivalent of 2.1log inactivation. This study indicated that the MPUV lamp was more effective than the LPUV lamp at reducing the subsequent photoreactivation of E.coli at the colony forming ability level after a 2log inactivation or both at the ESS and the colony forming ability levels after a 3log inactivation. This could be an attractive advantage of the MPUV lamp over conventional LPUV lamps.