The study found that Staphylococcus aureus lacking wall teichoic acids becomes much more resistant to two immune proteins (gIIA phospholipase A2 and human beta‑defensin 3), but its sensitivity to the antimicrobial peptide LL‑37 stays the same as normal bacteria. This suggests LL‑37 can still kill these bacteria even when they develop other resistance tricks.

Wall teichoic acids (WTAs) and membrane lipoteichoic acids (LTAs) are the major polyanionic polymers in the envelope of Staphylococcus aureus. WTAs in S. aureus play an important role in bacteriophage attachment and bacterial adherence to certain host cells, suggesting that WTAs are exposed on the cell surface and could also provide necessary binding sites for cationic antimicrobial peptides and proteins (CAMPs). Highly cationic mammalian group IIA phospholipase A(2) (gIIA PLA(2)) kills S. aureus at nanomolar concentrations by an action(s) that depends on initial electrostatic interactions, cell wall penetration, membrane phospholipid (PL) degradation, and activation of autolysins. A tagO mutant of S. aureus that lacks WTA is up to 100-fold more resistant to PL degradation and killing by gIIA PLA(2) and CAMP human beta-defensin 3 (HBD-3) but has the sensitivity of the wild type (wt) to other CAMPs, such as Magainin II amide, hNP1-3, LL-37, and lactoferrin. In contrast, there is little or no difference in either gIIA PLA(2) activity toward cell wall-depleted protoplasts of the wt and tagO strains of S. aureus or in binding of gIIA PLA(2) to wt and tagO strains. Scanning and transmission electron microscopy reveal increased surface protrusions in the S. aureus tagO mutant that might account for reduced activity of bound gIIA PLA(2) and HBD-3 toward the tagO mutant. In summary, the absence of WTA in S. aureus causes a selective increase in bacterial resistance to gIIA PLA(2) and HBD-3, the former apparently by reducing access and/or activity of bound antibacterial enzyme to the bacterial membrane.