Capsule specificity underpins the biology and translational potential of Klebsiella pneumoniae K16 phages

Klebsiella pneumoniae species complex (KPSC) is a leading cause of bloodstream infections (BSIs), with capsule diversity complicating vaccine development. Certain capsule types are disproportionately associated with disease, including the under-studied KL16. Here, we isolated and characterised four novel podophages that, despite encoding multiple depolymerases, exhibit strict K16 tropism. We show that selected phage M6 encodes two active depolymerases (K16-Dep46 and K16-Dep47), the first identified for this capsule type and the first example of a phage carrying dual enzymes with conserved substrate specificity. The phages infected all K16 strains tested, including clinical and environmental isolates from Malawi, the UK and Thailand, with diagnostic precision. Purified K16-Dep47 expanded the host range of other phages, enabling M6 to act in concert with capsule-independent phages, as well as with ceftazidime to improve bacterial clearance. These findings define the molecular basis of K16-phage specificity and highlight targeted phage isolation for therapeutic and diagnostic applications.