Broad-host-range Kayvirus phages preferentially infect Staphylocococcus aureus cells with β-glycosylated WTA, the most common bacterial form in the human host

• Myophage phiIPLA-RODI can infect a wide range of Staphylococcus aureus strains from different origins • The degree of phage susceptibility amongst these strains varies greatly, with some isolates requiring a very high MOI • These differences are due to mutations affecting WTA glycosylation and/or capsule production • This phenotype is regulated by the alternative sigma factor SigB and the agr quorum-sensing system In Staphylococcus aureus , WTA glycosylation participates in the interaction with the immune system and bacteriophage adsorption. Indeed, virulent phages with podovirus morphology and some myoviruses require β-glycosylation (catalized by TarS), and are hindered by α-glycosylation (carried out by TarM) of WTA. In contrast, other myophages, like phiIPLA-RODI and phage K, exhibit a broad-host range and infect strains without either glycosylation according to the spot test. Here, we demonstrate that these two phages, despite not requiring WTA glycosylation, are both significantly more efficient at infecting strains with tarS -mediated modifications. Moreover, presence of tarM correlates with decreased susceptibility to phiIPLA-RODI, especially in strains lacking an intact capsule. Besides confirming that mutations in the quorum-sensing system Agr confer reduced susceptibility to some phages, we also identified the alternative sigma factor SigB as an additional regulator of phage infectivity. While Agr controls transcription of tarM , SigB exerts this role by modulating tarS expression. Our results suggest that the majority of known virulent phages infecting S. aureus have evolved to maximize their chances of infecting this pathogen in the mammalian host. While this is good news from the perspective of phage therapy, the potential impact of altering the balance between phage and host by exposing cells to high doses of phages must be examined.