In Vivo Emergence of Podovirus Resistance via Mutation During Phage-Antibiotic Treatment of Experimental MSSA Endocarditis.

Phage therapy shows promise as an adjunct to antibiotics for treating Staphylococcus aureus infections. We previously reported a combined flucloxacillin/two-phage cocktail treatment selected for resistance to podovirus phage 66 in a rodent model of methicillin-susceptible (MSSA) endocarditis. Here we show that resistant clones harbor mutations in , which encodes a glycosyltransferase essential for β-GlcNAcylation of wall teichoic acid (WTA). This WTA modification has been described in vitro as critical for adsorption. Transcriptomics confirmed continued expression in resistant clones, supporting a loss-of-function mechanism. Accordingly, phage 66 binding and killing were restored by WT complementation. In addition, we investigated the counterintuitive innate susceptibility to phage 66 of the + Laus102 strain used in the endocarditis model. We show that it likely results from a significant lower expression, in contrast to the innate resistant strain RN4220. Our findings demonstrate that -mediated WTA β-GlcNAcylation is critical for podovirus infection also in vivo and identify transcriptional defect as a new mechanism of podoviruses susceptibility in . Moreover, and since disruption has been previously shown to enhance β-lactam susceptibility, our results support the development of combined podovirus/antibiotic strategies for the management of MRSA infections.