Iron requirement and chelator production of staphylococci,Streptococcus faecalis and enterobacteriaceae

The effect of iron deprivation on growth of 101 aerobic strains of gram-positive and gram-negative bacteria was studied on agar media in the presence of various concentrations of the synthetic iron chelator ethylene diamine diorthohydroxyphenyl acetic acid (EDDA) and the iron binding protein transferrin.Growth of Staphylococcus epidermidis was inhibited by 15mm EDDA and 1.5mm transferrin. Staphylococcus aureus was only inhibited by 44mm EDDA and not by transferrin. None of the strains of S. faecalis was inhibited. The majority of the enterobacteriaceae (E. coli, Salmonella spp, Klebsiella spp) was inhibited by 44mm EDDA and 1.5mm transferrin. The relation between susceptibility and concentration of EDDA and transferrin was expressed as S-value for each species. Iron supply with various iron compounds could restore the effects of inhibition.In all species except in S. faecalis iron chelator production could be demonstrated, using indicator plates of media containing EDDA and flooded with 10⁴–10⁵ colony forming units of indicator organisms.The iron chelator of both S. epidermidis and S. aureus could stimulate growth of S. epidermidis, but not that of enterobacteriaceae. Iron chelators from all gram-negative bacteria were functionally interchangeable, but did not stimulate growth of gram-positive bacteria.