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. 2008 Oct 13;76(12):5598–5607. doi: 10.1128/IAI.01180-08

FIG. 6.

FIG. 6.

Analysis of curli expression and adherence among selected European SF STEC O157:NM strains. (A) Curli detection by immunofluorescence microscopy. Phase-contrast and fluorescence micrographs are shown for the indicated strains stained for curli using an anticurli monoclonal antibody following culture on CFA medium at 37°C as described in Materials and Methods. (B) Adherence of selected strains to Caco-2 cells. The indicated strains were cultured on CFA agar, and their adherence to Caco-2 cells was determined after 2 h of incubation at 37°C. SF STEC O157:NM strain H8824 was included as a positive control. Microscopy was used to determine the number of bacteria per field for 30 fields. CR binding which correlates with curli expression (CFA, 37°C) is indicated for the strains below the graph. Error bars define standard deviations. Single asterisks indicate that, following culture on CFA agar, the CR-positive SF STEC O157:NM strain E02/879 adhered to Caco-2 cells at significantly higher levels than the CR-negative SF STEC O157:NM strains 340/97 and 080/01 (P < 0.001). Double asterisks indicate that, following culture on CFA agar, the CR-positive SF STEC O157:NM strain E06/486 adhered to Caco-2 cells at significantly higher levels than the CR-negative SF STEC O157:NM strains 340/97 and 080/01 (P < 0.01). (C) csgBAC and csgD promoter activity in selected strains. The indicated strains were transformed with plasmid-based promoter-GFP fusion constructs, and expression of csgBAC::gfp (shaded bars) and csgD::gfp (unshaded bars) was measured following the culture of transformed strains on CFA-CAM agar plates. Background fluorescence levels were determined for the promoterless plasmid pAJR70 and subtracted. The data are expressed as relative fluorescence units (RFU). Error bars indicate standard errors of the means. Single asterisks indicate that, following culture on CFA-CAM agar, expression from the csgBAC promoter for CR-positive SF STEC O157:NM strains E02/879, E06/486, and H8824 was significantly higher than that for CR-negative SF STEC O157:NM strain 340/97 (P < 0.02). Expression from the csgBAC promoter for strains E02/879 and H8824 was also significantly higher than that for strain 080/01 (P ≤ 0.002). Double asterisks indicate that, following culture on CFA-CAM agar, expression from the csgD promoter for strain H8824 was significantly higher than that for strains 340/97, 080/01, E02/879, and E06/486 (P < 0.001).