Indicators for photoreactivation and dark repair studies following ultraviolet disinfection

  • Puay Hoon Quek
  • Jiangyong Hu
Original Paper


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.


Dark repair Escherichia coli Indicators Photoreactivation Low- and medium-pressure ultraviolet disinfection Gel electrophoresis 



The authors wish to thank Ms Chua Koon Joo Jessica and Mr Ho Ming Wei for their assistance in conducting the study.


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Copyright information

© Society for Industrial Microbiology 2008

Authors and Affiliations

  1. 1.Division of Environmental Science and EngineeringNational University of SingaporeSingaporeSingapore
  2. 2.Division of Environmental Science and Engineering, Faculty of EngineeringNational University of SingaporeSingaporeSingapore

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