Removal of contaminants of emerging concern (CECs) is of utmost importance to achieve safe, sustainable drinking water treatment. Among biological CECs, pathogens resistant to disinfection are particularly problematic. While studies on bacterial resistance have mainly focused on pathogenic organisms that are innately resistant to disinfection, we report the possibility of bacteria developing resistance to disinfectants over the course of repeat exposures. In this work, hypochlorite and ferrate were studied as two different disinfectants. Ferrate (Fe(VI)) was tested as a promising candidate for a “greener” disinfectant because it lowers the risk associated with the generation of hazardous disinfectant byproducts. We performed laboratory experimental evolution in which separate cultures of E. coli were repeatedly exposed to ferrate and hypochlorite over multiple stress cycles. Our results showed that the repeated exposure to hypochlorite significantly reduced the log inactivation among stressed cells compared to non-stressed cultures, suggesting that the E. coli cells developed resistance to hypochlorite over time. This resistance was shown to be persistent for many generations even after hypochlorite exposure ceased. In contrast, there was no change in the log inactivation of bacterial cells exposed to ferrate. This suggests that the repeated exposure of E. coli cells to ferrate over an extended time period did not lead to the development of bacterial resistance. Additional experiments to elucidate the molecular mechanisms behind the resistance development or the lack thereof are currently underway. These results point to the potential of pathogens developing resistance over time to some disinfectants. In particular, these observations pose significant risk for “closed-loop” systems such as direct potable reuse and green building water reuse systems in which there is possibility of microbial regrowth in between disinfectant dosages. In such systems, alternative disinfectants such as ferrate may need to be considered to prevent the development of bacterial resistance.

Long-term development of bacterial resistance against disinfectants: Hypochlorite vs. ferrate

255th National Meeting (2018)

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