Characterization of atypical enteropathogenic Escherichia coli strains that express typical localized adherence in HeLa cells in the absence of the bundle-forming pilus

Abstract

The characterization of nine atypical enteropathogenic Escherichia coli strains expressing localized adherence in HeLa cells in the absence of the bundle-forming pilus revealed a diversity of serotypes, plasmids, and virulence genes. Although the strains lacked known E. coli adhesin genes, the identification of new adhesins could contribute to the characterization of similar enteropathogenic E. coli isolates.

FIG. 1.

Localized adherence patterns in HeLa cells of representative atypical EPEC strains that lack the bundle-forming pilus. (A) LA pattern (compact microcolonies, 3 h) of typical EPEC strain E2348/69; (B) LAL pattern (loose microcolonies, 6 h) of atypical EPEC strain 1711-4; (C to F) LA₆ (compact microcolonies, 6 h) of four representative atypical EPEC strains, namely, strain 0621-6 (C), strain 1331-2 (D), strain 1551-2 (E), and strain 1112-6 (F). Original magnification, ×1,000.

FIG. 2.

Transmission electron micrograph of HeLa cells infected with a representative atypical EPEC strain of a non-EPEC serogroup, i.e., strain 1551-2, that expresses typical localized adherence (LA₆) in the absence of the bundle-forming pilus. Note the pedestal-like structures that characterize the A/E lesions underneath intimate adherent bacteria, which were observed for all nine strains studied.

FIG. 3.

Plasmid contents of nine atypical EPEC strains of non-EPEC serogroups expressing typical localized adherence (LA₆) in HeLa cells in the absence of the bundle-forming pilus. Lanes: 1, strain 0471-1; 2, strain 0621-6; 3, strain 1331-2; 4, strain 1551-2; 5, strain 2041-1; 6, strain 1112-6; 7, strain 2932-2; 8, strain 3522-6; 9, strain 4632-3; 39R861, E. coli strain carrying plasmids of known molecular sizes.