Adhesion to and biofilm formation on polystyrene by 12 S. maltophilia isolates from CF patients. A. Adhesion (grey bars) and biofilm (black bars) levels were assessed by crystal violet colorimetric technique and expressed as optical density read at 492 nm (OD492). OBGTC26 strain adhesiveness was significantly higher than OBGTC49, OBGTC50, and OBGTC52 strains (* P < 0.05; Kruskall-Wallis test followed by Dunn's multiple comparison post-test). Biofilm formed by OBGTC20 strain was significantly higher than that produced by OBGTC9 and OBGTC49 strains (** P < 0.01; Kruskall-Wallis test followed by Dunn's multiple comparison post-test). Results are expressed as means + SDs. B. Relationship between adhesion to and biofilm formation levels on polystyrene. A statistically significant positive correlation was found between adhesion and biofilm levels (Pearson r = 0.641; P < 0.05).