A comparative toxicity evaluation of Escherichia coli-targeted ssDNA and chlorine in HepG2 cells

In this study, a comparative assessment of the effectiveness of ssDNA and chlorine as disinfectants for treating water contaminated with Escherichia coli (E. coli) was investigated on the basis of cytotoxicity and genotoxicity. The gene targets addressed for the ssDNA based inhibition method were marA (multiple antibiotic resistance) and groL (essential gene Hsp60) in E. coli. Based on the maximum log reduction in E. coli cell numbers when compared to no ssDNA control, groL-1 was chosen as the optimized ssDNA for gene silencing-based inactivation. For toxicity assessment, HepG2 cells were exposed to extracts corresponding to concentrations of 0.2, 1, 5, 25 and 50 mL water/mL medium of chlorine doped water and 1, 10, 100, 300 nM of ssDNA. Compared with ssDNA, HepG2 cells exposed to extracts of chlorine doped water for 24 h showed higher cytotoxicity, caspase 3/7 levels, DNA damage, micronuclei frequency, and decreased cell viability. Water doped with chlorine was found to be more toxic than that by ssDNA when exposed to HepG2 cells. The results of this study provide a scientific basis for comparative evaluation of new and conventional disinfection methods by taking into consideration the outcome of cytotoxicity and genotoxicity assessments.