Decay of Viral Indicator T7 Bacteriophage After Repeated Exposures to Chlorine and Heat Treatments

摘要

Free chlorine and thermal treatment are used in water disinfection, sludge treatment, and food sterilizationprocesses to inactivate pathogens. Previous research has shown that RNA viruses and bacteriophages can evolveto develop increased resistance to chlorination and thermal disinfection. However, DNA bacteriophages are alsocommonly used as indicators and surrogates for enteric viruses, but knowledge about their adaptation to disinfectionprocesses is more limited. We repeatedly subjected T7 coliphage to small doses of free chlorine or toheat treatment at 60℃ for a long enough time to cause an inactivation of 90–99.9%, then cultivated the survivingphage and assessed the resistance to these treatments to understand if increased resistance emerged. After10 repeated exposures to free chlorine, T7 coliphage did not develop increased resistance compared with theunexposed strain. However, T7 did develop an increased resistance to thermal treatment at 60℃ after fourconsecutive exposures. The heat-adapted population of T7 had a significantly lower decay rate than the originalstrain, but its breakpoint temperature (a measure of its thermal stability) did not change. Results from this studyprovide important implications for scientific and practitioner communities, specifically that not all bacteriophagesare equal indicators, proxies, or surrogates for human pathogens in all treatment processes, and cautionis warranted when choosing an appropriate indicator. Further research is needed to better understand theinfluence of virus genome type, mutation rate, and capsid reactivity on virus evolvability to chlorine and heattreatment processes.