Phage resistance impacts antibiotic susceptibility and virulence in Staphylococcus aureus

As antibiotic resistance continues to rise worldwide, phage therapy offers a promising solution by harnessing viruses that infect and kill bacteria. However, phage-resistance may develop, compromising therapy. Phage-resistance has primarily been linked to changes in major phage receptors that for the human pathogen Staphylococcus aureus are the cell-wall linked wall teichoic acids (WTA). To identify additional factors contributing to phage-resistance, S. aureus was evolved under selective pressure from lytic phages, including candidates from therapeutic phage cocktails, to obtain resistant clones. A third of the phage-resistant clones acquired mutations associated with cell-wall changes previously linked with phage resistance, namely in femA , involved in peptidoglycan crossbridge formation, and tagO , encoding the initiator of the WTA biosynthesis. The remaining clones had mutations in pathways not previously associated with phage-resistance, including nucleoside catabolism ( deoC1 ), polyamine import ( potAB ) and DNA/RNA replication ( cshA, ligA ), suggesting that phage-resistance may be associated with phage-driven host takeover. Antibiotic susceptibility and virulence were diversely affected by the mutations; mutations in tagO increased β-lactams sensitivity and attenuated virulence, whereas mutations in femA / ligA or cshA increased staphylococcal virulence in Galleria mellonella . This work demonstrates the involvement of several novel bacterial pathways in phage resistance, highlighting the complexity behind phage-bacterial interactions.