Iron supply of staphylococci and of micrococci by alpha-ketoacids.

Most of 232 strains of coagulase-negative staphylococci (CNS) belonging to 16 species, and nine strains of micrococci belonging to four species, could be distinguished by their growth on an iron-poor nutrient medium. alpha-Keto-/alpha-hydroxyacids, as primary metabolites, facilitated iron supply to CNS and micrococci under various iron-limited conditions, as detected by different bioassay methods. Twelve selected CNS strains and two micrococcal strains produced significant amounts of alpha-ketoacids in iron-poor liquid nutrient media. In particular, strains of Staphylococcus cohnii, S. xylosus and S. lentus unable to grow on iron-poor media, produced high amounts of pyruvic acid and alpha-ketoglutaric acid. In bioassays, the selected CNS strains being siderophore indicator strains were fed with alpha-ketoacids at different levels of iron limitation. Strains able to grow under iron deprivation appeared to produce additional siderophores such as staphyloferrins under iron stress. alpha-Keto-/alpha-hydroxyacids may be additionally active in the iron supply of CNS and micrococci.