Isolation of a bacteriophage and its depolymerase specific for K1 capsule of Klebsiella pneumoniae: implication in typing and treatment.

Klebsiella pneumoniae causing community-acquired pyogenic liver abscess complicated with metastatic meningitis and endophthalmitis has emerged recently, most frequently associated with the K1 capsular type. A bacteriophage (NTUH-K2044-K1-1) that infects K. pneumoniae NTUH-K2044 (capsular type K1) was isolated and characterized. The phage infected all K1 strains, and none of the strains with other capsular types. Capsule deletion mutants were not lysed by this phage, suggesting that the capsule was essential for phage infection. Complete genome sequencing revealed the phage was a novel phiKMV-like virus. The gene-encoding capsule depolymerase was identified. The recombinant enzyme demonstrated specific lysis of the K1 capsule. Treatment with the phage or the recombinant enzyme provided significantly increased survival in mice infected with NTUH-K2044 strain, including one treated after the detection of a neck abscess by imaging. No obvious disease was observed after administration of this phage in mice. Phage was retained at detectable levels in liver, spleen, brain, and blood 24 hours after administration in mice. These results demonstrate this phage and its capsule depolymerase exhibit specificity for capsular type K1 and can be used for the diagnosis and treatment of K1 K. pneumoniae infections.