Figure 6

Clinical RT106 isolates display collagen-dependent biofilm formation. (a) 21 clinical RT106 strains (blue circles) and 3 non-RT106 toxigenic C. difficile strains (VPI, BI-1, and 630 designated as green, yellow and black circles, respectively) were cultured in uncoated or collagen-coated (combined types I and III) plastic wells for 72 h. RT106 strains displayed variable levels of biofilm on abiotic plastic wells. (b) Relative changes in biofilm densities (ΔA_570nm) were determined by comparing A_570nm of crystal violet-stained biofilms formed on human collagen (combined types I and III) vs. on uncoated plastic wells. Filled blue circles denote P_value < 0.05 determined using Student’s t test to compare mean A_570nm by each strain on collagen-coated vs. uncoated wells. No difference in biofilm formation was observed when the reference C. difficile 630, BI-1 and VPI strains were cultured on wells with or without collagen. Overall, RT106 strains displayed denser biofilms on collagen-coated wells (One-sample one-tailed T-test; H_alt: mean ΔA_570nm > 0; H₀: mean ΔA_570nm = 0; P_value = 0.02038).