A Frameshift Mutation in Associated with Phage Resistance in .

Phage therapy is a potential and promising avenue for controlling the emergence and spread of multidrug-resistant (MDR) , however, the rapid development of anti-phage resistance has been identified as an obstacle to the development of phage therapy. Little is known about the mechanism employed by MDR strains and how they protect themselves from lytic phage predation in vitro and in vivo. In this study, comparative genomic analysis shows undecaprenyl-phosphate glucose-1-phosphate transferase (WcaJ), the initial enzyme catalyzing the biosynthesis of colanic acid, is necessary for the adsorption of phage 117 () to the host strain Kp36 to complete its lytic life cycle. In-frame deletion of alone was sufficient to provide phage 117 resistance in the Kp36 wild-type strain. Complementation assays demonstrated the susceptibility of phage 117, and the mucoid phenotype could be restored in the resistant strain Kp36-117R by expressing the wild-type version of . Remarkably, we found that bacterial mobile genetic elements ( and ) block phage 117 infections by disrupting the coding region of , thus preventing phage adsorption to its phage receptor. Further, we revealed that the wcaJ mutation likely occurred spontaneously rather than adapted by phage 117 predation under unfavorable environments. Taken together, our results address a crucial evolutionary question around the mechanisms of phage-host interactions, increasing our current understandings of anti-phage defense mechanisms in this important MDR pathogen.