Mechanism of salicylate-mediated inhibition of biofilm in Staphylococcus epidermidis

The inclusion of 5 mM salicylic acid (SAL) in medium inhibited both growth and biofilm production by Staphylococcus epidermidis by up to 55%. The inhibition was not due primarily to chelation of cations. Excess divalent cations restored growth and biofilm production in chelated medium and in medium containing EDTA but not in medium containing SAL. ELISA analyses demonstrated that SAL inhibited production of teichoic acid, slime-associated proteins, and type 1 antigen by as much as 95%. However, it inhibited polysaccharide/adhesin production by only 50%-a figure paralleling the reduction in growth. The equivalent inhibitory effects of SAL on a pair of isogenic strains, one of which was a polysaccharide/adhesin-deficient mutant, confirmed that the primary effect of SAL was a reduction in the production of biofilm components rather than a reduction in the retention of these components in the slime layer prior to assembly into a biofilm.