Comparisons on the evaluation methods of chlorine resistance fungi in drinking water

Chlorine disinfection is fundamental for ensuring microbial safety in drinking water systems. However, fungi pose significant pathogenic risks due to their substantially higher chlorine resistance compared to bacteria. Existing approaches for evaluating fungal chlorine resistance face challenges, including the absence of standardized protocols, labor-intensive procedures, prolonged experimental durations, and limited real-time detection capabilities. Moreover, the mechanisms underlying fungal chlorine resistance remain inadequately understood. This study provides a comprehensive and systematic comparison of the primary methods used to assess fungal chlorine resistance, including log reduction, concentration-time (CT) values, and minimum inhibitory concentration (MIC). The CT value method incorporates disinfectant decay, contact time, and experimental conditions to reflect the dynamics of the disinfection process. In contrast, the log reduction method focuses on endpoint inactivation, while MIC provides a retrospective evaluation. Therefore, the CT method is recommended as the most effective method. This study investigates the underlying mechanisms of fungal chlorine resistance, emphasizing the critical roles played by fungal cell wall components, such as melanin and chitosan, the antioxidant enzyme systems, and the formation of biofilms in conferring enhanced resistance to chlorine exposure. The findings provide a theoretical foundation for the development of standardized methods and more effective strategies for controlling fungal contamination in water treatment process.