Characterizing the bacteriophage PKp-V1 as a potential treatment for ESBL-producing hypervirulent K1 Klebsiella pneumoniae ST258 isolated from veterinary specimens.

Background and aim: The dearth of new antibiotics necessitates alternative approaches for managing infections caused by resistant superbugs. This study aimed to evaluate the lytic potential of the purified bacteriophage PKp-V1 against extended-spectrum β-lactamase (ESBL) harboring hypervirulent Klebsiella pneumoniae (hvKp)-K1 recovered from veterinary specimens.

Materials and methods: A total of 50 samples were collected from various veterinary specimens to isolate K. pneumoniae, followed by antimicrobial susceptibility testing and molecular detection of various virulence and ESBL genes. Multilocus sequence typing of the isolates was performed to identify prevalent sequence types. The bacteriophages were isolated using the double-agar overlay method and characterized using transmission electron microscopy, spot tests, plaque assays, stability tests, and one-step growth curve assays.

Results: Among 17 (34%) confirmed K. pneumoniae isolates, 6 (35%) were hvKp, whereas 13 (76%) isolates belonging to the K1 type were positive for the wzy (K1) virulence gene. All (100%) hvKp isolates exhibited the allelic profile of ST258. Overall, PKp-V1 exhibited an 88 % (15/17; (p ≤ 0.05) host range, among which all (100 %; p ≤ 0.01) hvKp isolates were susceptible to PKp-V1. PKp-V1 exhibited a lytic phage titer of 2.4 × 10⁸ plaque forming unit (PFU)/mL at temperatures ranging from 25°C to 37°C. The lytic phage titers of PKp-V1 at pH = 8 and 0.5% chloroform were 2.1 × 10⁸ PFU/mL and 7.2 × 10⁹ PFU/mL, respectively.

Conclusion: Although the incidence of ESBL-infected K. pneumoniae in veterinary settings is worrisome, PKp-V1 phages showed considerable lytic action against the host bacterium, indicating the potential of PKp-V1 as a possible alternative therapeutic option against MDR K. pneumoniae.