FIG. 2.

(A) aLf is bactericidal for S. aureus Newman. FeSO₄ or CaCl₂ was added to preparations of aLf used in killing assays prior to dialysis to remove excess salts. S. aureus Newman was treated with 0.5 μM aLf (▪), aLf plus 10 μM FeSO₄ (▴), or aLf plus 10 μM CaCl₂ (×). (B) Addition of rabbit anti-Lf antibodies inhibits Lf bactericidal activity. S. aureus Newman was treated with aLf and different dilutions of anti-Lf antibodies, including 1:10 (▪), 1:100 (▴), and 1:1,000 (⧫), as well as no anti-Lf antibody (•). (C) IsdA protects S. aureus Newman against killing by 0.5 μM aLf. The following strains were used: ▪, Newman (wild type); ▴, SRC105 (isdA); •, SRC105(pSRC001); ⧫, SRC105(pMK4); and ×, SRC150 (srtA). The data for strains Newman and SRC105(pSRC001) overlap extensively, as do the data for strains SRC105, SRC105(pMK4), and SRC150. (D) Addition of a molar excess of rIsdA, but not addition of a molar excess of rIsdAC, inhibits killing of S. aureus Newman by 0.5 μM aLf. Symbols: ▪, aLf; ▴, rIsdA plus aLf (5:1 molar excess); ▵, rIsdA plus aLf (10:1 molar excess); •, rIsdAC plus aLf (5:1 molar excess); ○, rIsdAC plus aLf (10:1 molar excess). In all panels, the values are the means of three independent experiments.