<b>Phage anti-defense genes targeting NAD</b>^{<strong>+ </strong>}<b>metabolism and DNA replication </b><b>expand</b><b>a broad host range against</b><b><i> </i></b><b><i>Klebsiella pneumoniae</i></b>

Phage therapy for drug-resistant Klebsiella pneumoniae (K. pneumoniae) is limited by narrow host ranges. We isolated a broad-host-range phage, vB_KP_P4, that lyses 109 diverse K. pneumoniae strains, including multidrug-resistant (MDR) and carbapenem-resistant isolates. We demonstrate that its lytic breadth is governed by its ability to overcome host intracellular defenses. We provide direct genetic evidence that three phage-encoded genes, deoxycytidylate deaminase (comEB), nicotinamide-nucleotide adenylyltransferase (nadM), and a DNA polymerase clamp loader (rfcS), are critical anti-defense determinants. Deletion of these genes collapsed the host spectrum from 109 strains to fewer than 10, abrogating antibacterial efficacy. The wild-type phage substantially improves survival in a mouse bacteremia model. Our study elucidates a key genetic basis for the broad host range, specifically targeting host immunity,and provides a new strategy for engineering therapeutic phages.