Molecular Based Assessments of Inactivation and Photorepair of Mycobacterium Terrae Following UV Disinfection
Abstract:UV irradiation is now a commonly accepted technology for water and wastewater disinfection. The resistance of Mycobacterium terrae to LP and MP UV irradiation was assessed using a bench-scale collimated beam system. The germicidal effectiveness of UV light correlates with the absorption spectrum of DNA, but some of the bacteria are able to repair the DNA damage caused by UV light. To assess photorepair, half of the irradiated M. terrae solution was plated immediately and the rest was exposed to photorepair conditions under a visible-light lamp using a quantified photo-repair light intensity and optimal exposure time. M. terrae were enumerated after photorepair and concentrated for subsequent DNA dimer damage analyses.
DNA was extracted from M. terrae and the endonuclease sensitive site (ESS) assay performed to assess UV light based damage. Using the cultivability assay, we found that the inactivation of M. terrae by LP UV was similar to the inactivation by MP UV (significance p = 0.79). Inactivation scaled logarithmically with UV fluence. Photorepair reduced the inactivation by 0.5 log on average, for both UV systems. Compared with E. coli B, the number of pyrimidine-damaged sites (ESS/kb) per UV fluence in M. terrae was lower. The rate of photorepair assessed by the ESS assay was similar to that estimated by the standard enumeration technique.
Document Type: Research Article
Publication date: January 1, 2005
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