Isolation and characterization of a potent bacteriophage KA targeting an antibiotic-resistant human pathogenic strain of Klebsiella pneumoniae KP1.

The escalating antibiotic resistance of Klebsiella pneumoniae has necessitated the exploration of alternative therapeutic strategies, with bacteriophages emerging as a promising option due to their specificity and non-toxic nature. This study focused on the isolation and characterization of the lytic KA bacteriophage, which demonstrates efficacy against the multi-drug resistant human pathogenic strain K. pneumoniae KP1. The KA bacteriophage exhibits an icosahedral morphology with a short non-contractile tail, and its genome comprises 49,319 base pairs encoding 54 proteins. Notably, it lacks genes associated with lysogeny, virulence, or antibiotic resistance. It is classified within the Autographiviridae family, Slopekvirinae sub-family, and Drulisvirus genus, and represents a novel species with less than 95 % sequence similarity to previously identified phages in the NCBI database. The KA phage maintained stability between -4 and 40 °C and pH 4-8, with an optimal multiplicity of infection (MOI) of 1, a latent period of 40 min, and a burst size of 80 plaque forming units (PFU) per infected cell. The presence of calcium chloride and magnesium chloride reduced the adsorption time of the KA phage. It was active against 7 out of 15 strains of K. pneumoniae but did not affect Escherichia coli and Pseudomonas aeruginosa. The most effective eradication of the host bacterium by the KA phage occurred at MOI 10 and 1, after 60 and 90 min of incubation in tryptic soy broth at 35 °C and pH 7. Furthermore, the KA phage removed 84 % of host bacteria from a contaminated glass slide after 1 h of incubation at MOI 10. These findings suggest that the KA phage could serve as a potential treatment for pneumonia caused by multi-drug resistant K. pneumoniae, pending further investigation into its in vivo safety and stability.