Evaluating Curli Production in E. coli Strains

Curli production was determined in the strains by Congo Red assay as previously described (Zhou et al., 2013 (link)). Congo Red agar plates was made by preparing yeast extract and Casamino acid agar (YESCA; 1 g L^-1 yeast extract, 10 g L^-1 casamino acids, 20 g L^-1 agar) and after autoclaving, filter sterilized Congo Red (50 μg ml^-1 final concentration; Sigma) and filter sterilized Brilliant Blue G (10 μg ml^-1 final concentration; Sigma) were added. E. coli strains were grown in LB broth and incubated at 37°C overnight. Five microliters of the overnight culture of each strain was spotted on the center of a thick Congo Red agar plate. The plates were incubated at 28°C for 48 h. Images were captured with Canon CanoScan 9000F MKII Flatbed Scanner at 600 dpi.