Receptor Analysis

To verify the receptor, S. aureus RN4220, a strain free of prophages (Kreiswirth et al., 1983), type I restriction mechanisms, and capsules (Wann et al., 1999), was utilized (Table 1). It is known that most genetic manipulation of S. aureus is confined to strain RN4220 because RN4220 is defective of type I restriction–modification (RM) system, whereas different lineages of S. aureus contain a unique pair of type I RM systems (Cooper et al., 2017). We obtained an RN4220ΔtagO:erm mutant, which lacks the peptidoglycan-anchored wall teichoic acid (WTA) (Swoboda et al., 2010), and its complemented strain carrying the pStagO plasmid. This plasmid was constructed by subcloning the tagO gene into an Escherichia coli–S. aureus shuttle expression vector, pND50 (Brückner, 1992). Afterward, 10 μL of 10-fold diluted phage PALS2 lysate (10¹⁰ to 10³ PFUs/mL) was spotted from top–left to bottom–right on soft agar (TSB containing 0.4% agar), beginning with the highest titer, with the wild-type RN4220, the RN4220ΔtagO:erm mutant, and the tagO-complemented strain.