Staphylococcus aureus adaptation to vancomycin influences phage susceptibility.

Phages are bacterial viruses considered as therapeutics for treatment of serious infections with antibiotic-resistant pathogens. In Staphylococcus aureus, resistance to cell wall targeting antibiotics is common in the methicillin resistant (MRSA) or vancomycin-intermediate susceptible (VISA) strains. Furthermore, the cell wall anchors the primary phage receptor, the wall teichoic acid (WTA) glycopolymers. Here we demonstrate that mutations resulting in VISA development affect phage susceptibility of clinically and laboratory evolved strains. For clinical strains we observed both increased and decreased susceptibility compared to the ancestral vancomycin susceptible strains when infected with the therapeutically relevant myoviruses, ΦIPLA-RODI, Stab20, Stab21 and ΦK. For laboratory strains adapted to vancomycin from the MRSA strain, JE2, we observed variable resistance development to the phages ΦIPLA-RODI, Stab21 and ΦK with one strain becoming completely phage resistant. In contrast, half of the VISA strains became susceptible to Stab20 to which JE2 is resistant. These changes in part correlated with altered WTA glycosylation patterns as shown by WTA-specific antibodies and for the resistant strain resulted in compromised phage therapy as shown in a Galleria mellonella infection model. This study highlights the need for understanding antibiotic-driven alterations in bacterial physiology when developing phage-based therapies using combination treatments with antibiotics and phages.