Hypervirulent Klebsiella pneumoniae with a hypermucoviscosity phenotype challenges strategies of water disinfection for its capsular polysaccharides

Due to the strong pathogenicity of hypervirulent Klebsiella pneumoniae (hvKP), its performance against disinfectants in water should be understood to protect public health and ecological environment. Unfortunately, the disinfectant tolerance of hvKP with a hypermucoviscosity (HMV) phenotype is a critical underexplored area. Here, the tolerance of K. pneumoniae isolates to common disinfectants was evaluated, and its underlying mechanisms were clarified. Results showed that hvKP strains with HMV exhibited remarkable tolerance to triclosan (TCS), sodium hypochlorite (NaClO), and benzalkonium bromide (BB), surpassing that of low-virulent K. pneumoniae (lvKP) and Escherichia coli, which is the microbial indicator of drinking water quality. Ct value of NaClO reached 4.41 mg/L·min to kill 4-log hvKP, while the values were 2.52 and 2.28 mg/L·min to achieve 4-log killing of lvKP and E. coli, respectively. The curing of the virulence plasmid from hvKP strain K2044 revealed that capsular polysaccharide (CPS) synthesis, driven by the virulence plasmids, helped mitigate cell membrane injury and bacterial inactivation under NaClO stress; consequently, it provided a protective advantage to hvKP. Enhancing the antioxidative stress system to reduce ROS production and mitigate oxidative stress caused by NaClO further improved the disinfectant resistance of hvKP strains with HMV. This study emphasized that hvKP strains with HMV posed a considerable challenge to disinfection procedure of water treatment. It also revealed that an improved dosage of NaClO ensures bacteria killing, indicating the optimization of the design of water treatment processes involving disinfection strategies and technical parameters should be considered.