Variations in the csgD promoter of Escherichia coli O157:H7 associated with increased virulence in mice and increased invasion of HEp-2 cells

Abstract

Promoter alterations in the csgD gene of Escherichia coli O157:H7 strains ATCC 43894 and ATCC 43895 are associated with variations in curli expression and the ability to bind Congo red dye. Red variants of each strain were more invasive for cultured HEp-2 cells than were white variants. An ATCC 43895 red variant was more virulent than a white variant in a mouse model. However, there were no differences in Shiga toxin production between red and white variants.

FIG. 1.

Comparative percentage of HEp-2 cell invasion (with 95% confidence intervals [error bars]) by various bacterial strains. The number in parentheses below each strain is the number of experimental replicates. EHEC, enterohemorrhagic E. coli.

FIG. 2.

Confocal microscopic image of HEp-2 cells infected with the ATCC 43895 Congo red-binding variant. The optical section includes an intracellular plane that contains numerous bacterial cells adjacent to nuclei.

FIG. 3.

Survival curves of (A) and fecal shedding by (B) CD-1 mice orally challenged with red or white variants of streptomycin-resistant ATCC 43895 E. coli O157:H7 (concentration, 10⁹ CFU/ml) compared to those of control mice (LB broth). Control mice did not shed E. coli O157:H7; each data point represents an individual mouse. There were seven mice per group.

FIG. 4.

Comparative Vero cell Stx assay for red (curliated) and white (noncurliated) variants of ATCC 43895 E. coli O157:H7. NC, negative control; PC, positive control.