Interaction of different Shiga toxin-producing Escherichia coli serotypes with Caco-2 cells

Shiga toxin-producing Escherichia coli (STEC) is defined by the ability to produce one or more types of Shiga toxins. In an attempt to better understand the mechanisms that underlie pathogenicity among STEC foodborne infection, we compared different STEC serotypes recovered from food sources (O26:H11, O103:H2, and O157:H7) for their interaction with human intestinal epithelial cells using the Caco-2 cell line as an infection model. Bacterial uptake was determined using gentamicin protection assay and results were confirmed by fluorescent microscopy. Our results revealed no significant difference in adherence among tested serotypes. Nonetheless, E. coli O157:H7 exhibited a significant increase of internalization ability and survived significantly better over different time points for up to 24 h. To study cellular invasion mechanisms, multiple inhibitors with known effects on eukaryotic cell structures and processes were used. Inhibition of bacterial and host cell protein synthesis significantly diminished entry in all tested serotypes, suggesting that invasion is an active process that requires both bacterial and eukaryotic protein syntheses. Cytochalasin D (an actin microfilament inhibitor) and staurosporine (inhibitor of several protein kinases) significantly decreased internalization of all tested serotypes. Our results suggested that invasion by STEC varies between different serotypes, might correlate with clinical outcome, and is receptor mediated. This process is dependent on microfilament-dependent pathway and phosphorylation of cell proteins but not on formation of microtubules.