Characterization and Therapeutic Potential of Three Depolymerases Against K54 Capsular-Type Klebsiella pneumoniae.

Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKp), a pathogen causing severe nosocomial infections and high mortality rates, is increasingly becoming a serious global public health threat. Capsular polysaccharide (CPS), a major virulence factor of hvKp, can be enzymatically degraded by bacteriophage-derived depolymerases. However, to our knowledge, depolymerases targeting K. pneumoniae K54-type strains have rarely been identified. Here, we identified and characterized three novel capsule depolymerases, Dep_C, Dep_Y, and Dep_Z, derived from three different K. pneumoniae phages, which retained robust activity across a broad pH range (pH 3.0-12.0) and demonstrated thermal stability up to 50 °C. These depolymerases could efficiently digest the CPS of K. pneumoniae K54-serotype strains, significantly inhibit biofilm formation, and remove their mature biofilms. Although no bactericidal activity was detected, these depolymerases rendered host bacteria susceptible to serum complement-mediated killing. We further demonstrate that Dep_C, Dep_Y, and Dep_Z can effectively and significantly prolong the survival time of mice in a pneumonia model infected with K54-type K. pneumoniae and reduce the colonization and virulence of the bacteria in the mice. These findings indicate that depolymerases Dep_C, Dep_Y, and Dep_Z could increase bacterial susceptibility to host immune responses of hvKp to the host through their degradation effect on the CPS. In conclusion, our study demonstrates that the three capsule depolymerases are promising antivirulent agents to combat CR-hvKp infections.