Phenotypic Characterization and Preliminary In Vivo Evaluation of a Locally Isolated Klebsiella pneumoniae Bacteriophage

Drug-resistant Klebsiella pneumoniae is a serious clinical problem, and bacteriophages are being investigated again as antibacterial agents. This study describes the phenotypic characterization and a preliminary in vivo evaluation of vB_Kpn_NIIPB-V0006, a bacteriophage isolated locally on a drug-resistant clinical K. pneumoniae strain. The genome of the phage was not sequenced. It has therefore not been screened for lysogeny-associated, toxin, virulence or antimicrobial resistance genes, and the results below describe what the phage does, not whether it is suitable for therapy. We assessed plaque morphology, specific lytic activity, titer, host range on a limited non-target panel, particle morphology, adsorption, one-step growth, chloroform exposure, the frequency of phage-resistant host variants, endotoxin reduction, short-term safety in mice and antibacterial effect in guinea pigs. The phage lysed the target strain, with an Appelman activity of 10⁻⁸ and a titer of 1.7 × 10¹¹ PFU/mL. Processing with 1-octanol lowered endotoxin content from 1200 to 12 EU/mL and preserved 80% of infective activity. Mice given the preparation intraperitoneally showed no mortality and no visible acute toxicity over 14 days. In guinea pigs with systemic K. pneumoniae infection, survival was the primary outcome: 0.5 mL three times daily gave 6/6 survivors against 1/6 in untreated controls (p = 0.015). Splenic bacterial burden, a secondary outcome, was also lower in that group (2.64 against 4.41 log₁₀ CFU/g). Two features of the design bias this second comparison in favor of treatment, since survivors and non-survivors were sampled at different times, and phage being carried over into the plating step is likely to have lowered colony counts. The 1.77 log₁₀ difference should therefore be read as an upper bound. The phage merits further study, but whole-genome sequencing, confirmation of the host species, host-range testing against diverse clinical isolates and a controlled comparison with antibiotic treatment are all needed before any therapeutic claim can be made.