DNA Repair of UV-irradiated G. lamblia Cysts Following Low and Medium Pressure UV Disinfection

University Of Washington, Seattle WA

Investigators

Abstract

0302609 Shin Ultraviolet (UV) irradiation has recently gained considerable attention as an alternative to conventional chemical disinfectants in water treatment processes after the recent discovery of its remarkable inactivation ability of the highly chlorine-resistant protozoan pathogens: Cryptosporidium parvum oocysts and Giardia lamblia cysts and relatively low potential of producing harmful disinfection byproducts (DBPs). In fact, UV disinfection is one of the most promising candidate technologies for compliance with the Stage 2 Disinfectants and Disinfection Byproduct Rule (DBPR) and Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). Despite the recently recognized promise of UV disinfection, however, there are still several issues that must be addressed before widespread use of UV irradiation as a primary disinfectant to achieve microbially-acceptable drinking water. One such issue is the ability of UV-irradiated waterborne pathogens to repair their UV-damaged DNA. Recently, our preliminary study indicates that G. lamblia cysts can restore their infectivity when they were exposed to low doses of low pressure UV and subjected to certain repair conditions. It is important to characterize the extent and kinetics of DNA repair in UV-irradiated G. lamblia cysts and then identify the threshold UV dosage for this microorganism in order to reduce the level of this important waterborne microorganism in drinking water by an acceptable level. Therefore, the objective of this proposed activity is to determine the kinetics and the extent of the DNA repair capabilities of UV-irradiated G. lamblia cysts after exposure to from low and medium pressure UV sources with both animal and molecular biological assays order to identify required dosages (threshold dosages) of both UV irradiation and thereby optimize UV disinfection processes to inactivate this important waterborne microorganism by an appreciable and acceptable level. This proposed activity is one of the rare studies on DNA repair in protozoans and probably the first study to characterize the mechanism and kinetics of UV inactivation and subsequent repair in these microorganisms using various molecular biological methods. The information gathered in this proposed activity will enable us to elucidate the different mechanisms of UV damage and repair phenomenon in UV-irradiated G. lamblia after low and medium pressure UV exposure. Furthermore, this information will help us to determine the threshold UV dosages for control of G. lamblia cysts for both LP and MP UV technology which will ensure low or no DNA repair of G. lamblia cysts and thereby optimize the effective doses of UV irradiation to inactivate this important waterborne microorganism to levels that will protect public health. Information about the primary UV damage and repair mechanisms for each type of UV lamps would make it possible to design current treatment facilities and future UV technology for maximal inactivation and repair inhibition against G. lamblia cysts and other waterborne protozoan parasites, and also would provide another important selection criteria for UV lamp type in a water treatment plant by comparing their potential advantages. Finally, the information and experience gathered in this proposed activity with G. lamblia cysts will be easily transferred to future studies on mechanisms of UV inactivation and repair phenomena in other new and emerging waterborne protozoan parasites.