Phage-Borne Depolymerases Decrease Klebsiella pneumoniae Resistance to Innate Defense Mechanisms.

Area of Science:

• Microbiology and Virology
• Bacterial Pathogenesis
• Immunology

Background:

• Klebsiella pneumoniae utilizes capsular polysaccharides as a key virulence factor, shielding it from host innate immune responses.
• Bacteriophages encode virion-associated depolymerases that degrade bacterial capsules, representing a potential strategy to combat bacterial infections.

Purpose of the Study:

• To characterize the capsule depolymerases KP32gp37 and KP32gp38 from Klebsiella phage KP32.
• To investigate the role of these depolymerases in determining the phage's host spectrum and their impact on K. pneumoniae virulence.

Main Methods:

• Biochemical characterization of depolymerase structure, thermostability, and optimal functioning conditions.
• Assessment of depolymerase activity on K. pneumoniae serotypes K3 and K21.
• Evaluation of depolymerase effects on bacterial resistance to complement-mediated killing, phagocytosis, and intracellular survival.
• In vivo testing using Galleria mellonella infection models.

Main Results:

• KP32 phage produces two specific capsule depolymerases, KP32gp37 (K3) and KP32gp38 (K21), defining its host range.
• Depolymerase treatment significantly reduced K. pneumoniae virulence, increasing susceptibility to complement-mediated killing (up to 4-log reduction) and phagocytosis (2-fold increase).
• Pre-treatment with depolymerases markedly decreased intracellular survival of bacteria within macrophages and improved survival rates in Galleria mellonella larvae.

Conclusions:

• Capsule depolymerases KP32gp37 and KP32gp38 effectively degrade Klebsiella pneumoniae capsules, neutralizing a major virulence factor.
• These depolymerases enhance bacterial susceptibility to innate immune mechanisms, demonstrating significant antivirulence potential.
• Bacteriophage-derived depolymerases represent a promising therapeutic strategy against K. pneumoniae infections.