Antibiofilm ability of the Trp-rich peptides (Table 1) against 24-h preformed biofilms of S. aureus USA300. Panels A–G were stained with crystal violet, while panels H–N were stained with XTT (see the text for further details). Thus, there are two panels for each peptide: peptide TetraF2W-RR (WT), panels A & H; W1R, B & I; W2R, C & J; W3R, D & K; L4R, E & L; I7R, F & M; W8R, G & N. P values were calculated based on paired Student’s t-test with two tailed distribution. P values <0.05 were considered significant (*).