• Haemin;
  • Staphylococcus aureus;
  • Metalloporphyrin;
  • X-ray microanalysis;
  • Potassium;
  • Ultrastructure

Abstract The unique antibacterial properties of Fe-protoporphyrin (haemin) on Staphylococcus aureus, compared to Co-protoprophyrin (Co-PP), Mg-protoporphyrin (Mg-PP) and Zn-protoporphyrin (Zn-PP) are described. Only haemin (20 μM) exhibits a strong light-independent antibacterial effect on S. aureus; the other metalloporphyrins, Co-PP, Mg-PP or Zn-PP, have no antibacterial effect in the dark. Only light photosensitization of Mg-PP-treated cells resulted in the inhibition of the bacterial growth, while Co-PP or Zn-PP were photodynamically inactive. A notable effect of haemin on inactivation of S. aureus was the induction of immediate ion fluxes as determined by X-ray microanalysis (XRMA) of fast-frozen cells. A marked efflux of K (96%) and Cl (94%) was expressed immediately as determined by X-ray microanalysis of S. aureus cells treated with haemin for 5 min. Only 48% loss of Na was detected in the cells under these treatment conditions, while P content was increased by 150%. Electron microscopy analysis revealed the appearance of a mesosome-like structure connected to the new septa, filmentous chromosome and arrays of aggregated ribosomes in the cytoplasm. We propose that haemin has multiple cellular targets for its oxidative effect in S. aureus.