Enterocyte-like Caco-2 cells as a model for in vitro studies of diarrhoeagenic Providencia alcalifaciens invasion

The entry of Providencia alcalifaciens into the enterocyte-like cell line Caco-2 compared to HEp-2 was studied. Of the 22 P. alcalifaciens strains, 13 and 21 were invasive for Caco-2 and HEp-2 cells, respectively. In contrast to HEp-2 cells, P. alcalifaciens was internalised by Caco-2 cells via receptor-mediated endocytosis. Tyrosine kinases play an important role in P. alcalifaciens uptake, also microfilaments and microtubules are engaged in this process. Inhibition of endosome acidification by ammonium chloride did not seem to have any significant effect on P. alcalifaciens invasion. Similarly to Shigella flexnerii, the invasion of Caco-2 cells by these bacteria occurred more effectively through the basolateral pole than through the apical surface of these cells. Plasmid DNA analysis showed the presence of plasmids of 5-172 kb in 13 strains regardless of their invasive ability. The presence of extracellular bacterial protein, most likely a kind of an invasin, is required for the invasion of Caco-2 and HEp-2 cells.