Chlorine Photolysis: A Step Forward in Inactivating Acanthamoeba and Their Endosymbiont Bacteria

Abstract

Chlorine and solar disinfection are widely used disinfectants in water treatment. However, certain potential pathogens can resist these methods, posing a public health risk. One such case is Acanthamoeba, a resistant free-living amoeba that protects pathogens inside from disinfection, thus endangering the health of water users. This work is the first evaluation of the inactivation efficiency achieved by combining NaClO (Cl2) and solar radiation (SR) against two Acanthamoeba strains from different sources (freshwater and pool water) and their endosymbiont bacteria (EB). Amoebae were exposed to different Cl2 doses (0–500 mg/L), SR wavelength ranges (280–800 nm and 320–800 nm), used as gold standards, and their combinations. The EB exhibited resistance to conventional Cl2 and SR treatments, requiring up to 20 times higher disinfectant doses than those needed to inactivate their protective Acanthamoeba. The pool strain and its EB demonstrated greater resistance to all treatments compared to the freshwater strain. Treatments with Cl2 (5 mg/L)/SR280–800nm completely inactivated both Acanthamoeba and EB of the freshwater strain, reducing up to 100 times the necessary Cl2 doses, suggesting that chlorine photolysis is an attractive treatment for disinfecting freshwater and preventing waterborne diseases associated with Acanthamoebae and its EB.