Comparison of biofilm-formation capacity in ten uspC–IS30–flhDC-positive waste water strains and eight uspC–IS30–flhDC-negative human faecal E. coli strains. Absorbance at 550 nm was used as a measure of biofilm formation capacity in biofilm formation assay. The result demonstrated that the biofilm-forming capacity of the naturalised waste water strains (uspC–IS30–flhDC positive) was significantly greater (asterisk represents p value < 0·1) than that of the human faecal strains (uspC–IS30–flhDC negative). For the box and whisker plots, the median values are represented by a thick line, the box represents the 25th and 75th percentiles and the whiskers are the upper and lower values