Reactivation of Pathogens

The effect of photoreactivation can be quite important in terms of operational cost (i.e., UV dosage) and disinfection efficiency. Knudson reported that the UV dose was 10 mJ/cm for a 3-log inactivated E. coli in the absence of photorepair however, the dose significantly increased to 25 mJ/cm in the presence of photorepair (15). The photoreactivation increased the UV dose necessary to achieve 3-log inactivation of seven Legionella species between 1.1- and 6.3-fold. However, certain germs such as C. parvum caimot be reactivated through the photorepair mechanism (16). RNA viruses lack the ability to photorepair in a host cell. 

Based on the difference in UV sensitivity of repair proficient and deficient bacteria, Jagger discovered that roughly 99% of repair is due to the dark repair (17). Unlike bacteria, viruses do not have the enzymes necessary for dark repair. However, virus can repair in the host cell using the host cell s enzymes (18). 

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