Epigallocatechin gallate (EGCg), the main polyphenol component of green tea, has several antibacterial properties. Here we show that sub-MICs of EGCg appear to decrease slime production, therefore inhibiting biofilm formation by ocular staphylococcal isolates previously characterized for the presence of ica genes by the Congo red agar plate assay and for adhesion to microtiter plates.Biofilm formation is a three-stage process (6) that significantly contributes to the pathogenesis of staphylococcal infections. The first stage, docking, is mainly due to hydrophobic interactions, whereas the next two stages, locking and maturation, are mediated by capsular polysaccharide adhesins, PIA (polysaccharide intercellular adhesin) and PNAG (poly-Nacetylglucosamine polysaccharide), both of which are synthesized by the gene products of the ica operon (icaADBC), with the main contribution coming from an N-acetylglucosaminyltransferase encoded by the icaA gene (5, 12). The expression of the icaA gene alone results in low enzymatic activity, but coexpression with icaD leads to a significant increase in activity (8).Green tea polyphenols and, more specifically, epigallocatechin gallate (EGCg) are known to possess both direct bactericidal activity (18,19) and the ability to potentiate the effects of certain antibiotics (15,16,17,21). Moreover, they have already been shown to have at least an indirect influence on biofilm production, in that they can retard the formation of dental plaque (9,11,20).In this study, we have investigated the effects of sub-MICs of EGCg (99% pure; Sigma) ( Fig. 1A, inset) on biofilm formation by 20 different ocular staphylococcal isolates derived from patients with community-acquired ocular infections and belonging to our private collection. The different isolates included 8 Staphylococcus aureus isolates and 12 Staphylococcus epidermidis isolates. Moreover, two American Type Culture Collection strains (S. epidermidis ATCC 35984 and S. epidermidis ATCC 12228) were used as reference controls. Table 1 summarizes the characterization of bacterial isolates for biofilm production. The MIC of EGCg for each strain was determined in tryptic soy broth (TSB) by a broth dilution method according to the guidelines of the CLSI (formerly the NCCLS) (13). The quality of the lot of EGCg was controlled by reverse-phase high-pressure liquid chromatography (HPLC) and showed just one single, sharp peak, suggesting a very high degree of purity (Fig. 1A). The MICs obtained ranged from 125 to 500 mg/ml, similar to that which we reported recently (17); however, they were slightly higher than those already described by other authors (22, 24).Each ocular isolate was then characterized for biofilm-related properties. Biofilm-forming ability was tested by determination of adhesion to microtiter plates (5) and was quantitated by safranin staining and reading of the absorbance at 492 nm. The biofilm production of the different strains was then arbitrarily classified as strong (optical density [OD], Ͼ0.9 OD), medium (0.6 Ͻ OD Ͻ 0.9),...