title: XF-73, a novel antistaphylococcal membrane-active agent with rapid bactericidal activity.
abstract: OBJECTIVE
  XF-73 is a novel porphyrin antibacterial agent previously reported to inhibit a range of gram-positive bacterial species, including Staphylococcus aureus. Its mode of action is unknown. Using S. aureus as a model organism we sought to examine the basis of its antibacterial activity.
  
  
  METHODS
  The effects of XF-73 on the growth and survival of S. aureus SH1000 were investigated by viable count and culture absorbance techniques. Inhibition of macromolecular synthesis and disruption of membrane integrity after exposure to XF-73 were examined by radiolabelling experiments, the BacLight fluorescent dye assay and measurement of K(+) and ATP leakage from the cell. The effect of XF-73 on a staphylococcal coupled transcription-translation system was also investigated.
  
  
  RESULTS
  XF-73 was rapidly bactericidal against S. aureus SH1000 and demonstrated more rapid killing kinetics than all other comparator agents when tested at an equivalent multiple (4x) of the MIC. Exposure of S. aureus to XF-73 for 10 min completely inhibited DNA, RNA and protein synthesis. XF-73 had no effect on transcription and translation in vitro. Cells exposed to XF-73 gave a positive response in the BacLight assay, which detects membrane damage. The drug also caused substantial loss of K(+) and ATP from the cell, but did not promote bacterial lysis.
  
  
  CONCLUSIONS
  XF-73 exhibited rapid membrane-perturbing activity, which is likely to be responsible for inhibition of macromolecular synthesis and the death of staphylococci exposed to the drug.
authors.affiliation: Antimicrobial Research Centre and Institute of Molecular and Cellular Biology, University of Leeds, Leeds, UK.
authors.forename: Nicola
authors.initials: N
authors.lastname: Ooi
authors.forename: Keith
authors.initials: K
authors.lastname: Miller
authors.forename: Joanne
authors.initials: J
authors.lastname: Hobbs
authors.forename: William
authors.initials: W
authors.lastname: Rhys-Williams
authors.forename: William
authors.initials: W
authors.lastname: Love
authors.forename: Ian
authors.initials: I
authors.lastname: Chopra
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000096:biosynthesis; D018533:Biomass; D002462:Cell Membrane / Q000187:drug effects*; D015169:Colony Count, Microbial; D003600:Cytosol / Q000737:chemistry; D004269:DNA, Bacterial / Q000096:biosynthesis; D006801:Humans; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects*; D015394:Molecular Structure; D011166:Porphyrins / Q000494:pharmacology*; D011188:Potassium / Q000032:analysis; D014176:Protein Biosynthesis / Q000187:drug effects; D012329:RNA, Bacterial / Q000096:biosynthesis; D011868:Radioisotopes / Q000378:metabolism; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D011166:Porphyrins; D012329:RNA, Bacterial; D011868:Radioisotopes; C521987:XF73 compound; D000255:Adenosine Triphosphate; D011188:Potassium