Regulation of slime production in Staphylococcus epidermidis by iron limitation.

Slime production by most strains of Staphylococcus epidermidis was enhanced by conditions of iron limitation produced by the addition of ethylenediamine-di-o-hydroxyphenol acetic acid to the growth medium. The density of the biofilm which formed on the base of microtiter plates was dependent on the degree of iron limitation, the stage of the growth cycle, and the nutritional state of the initial inoculum. One repeatedly slime-negative S. epidermidis strain, passaged in tryptic soya broth containing ethylenediamine-di-o-hydroxyphenol acetic acid, expressed high levels of slime after two passages. These observations suggest that iron limitation is one factor that regulates slime production by S. epidermidis. These findings could explain inconsistencies between the in vivo observation that biofilms invariably form on implanted catheters and the in vitro finding that some isolates from catheter-associated infection fail to produce slime.