Novel Autographivirales phages Kiwi, Nika and Pie targeting Klebsiella pneumoniae K14: Isolation, characterisation, genome analysis and study of the bacterial polysaccharide degradation.

Klebsiella pneumoniae is a significant pathogen responsible for a range of infections, including pneumonia, urinary tract infections, and sepsis, in both human and veterinary medicine. The extracellular polysaccharide produced by this bacterium forms a capsule that protects the cell from immune responses and external influences, complicating treatment. The World Health Organization has placed this pathogen into the ESKAPE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) of pathogens that require special attention due to their resistance to multiple drugs, and hypermucoid K. pneumoniae strains with prevalent capsular types (e.g., K1 and K2) have been extensively studied. However, rare capsular types that are less well-characterised can still pose significant challenges. In the present study, we isolated a K. pneumoniae strain with capsular type K14, which is associated with antibiotic-resistant urogenital infections in felines, from a veterinary clinic. We successfully isolated and characterised three bacteriophages that exhibit rapid adsorption to and efficient lysis of the bacterium. All three phages demonstrated strictly lytic behavior and proved effective in degrading the extracellular polysaccharide capsule of the pathogen. We have modelled the receptor-binding proteins of these phages, which exhibit depolymerising activity. These proteins were produced in recombinant form, and experimental evidence has demonstrated their capacity to cleave the polysaccharide associated with the K14 capsular type. Furthermore, the chemical structure of the resulting cleavage products was determined. All three phages have been thoroughly characterised and show potential for application in combating multidrug-resistant K. pneumoniae.