FIG 1.

Invasion of Caco-2 and HEp-2 cell monolayers. The level of invasion of both the Caco-2 and HEp-2 cell monolayers by the strains is expressed as the number of CFU per milliliter. ED97 and ED32 displayed the ability to invade the monolayers of both Caco-2 (A) and HEp-2 (B) cells, and the inactivation of the gene tia in strain ED32 Δtia strongly reduced the invasion ability. Complementation of the tia mutation restored the invasive phenotype of ED32. The difference between strain ED32 Δtia and both the ED32 and ED32 Δtia/pGEM_tia strains was statistically significant with a P value of <0.01, indicated by the asterisk. The expression of tia in the laboratory strain JM109 conferred only a moderate ability to invade the Caco-2 cell monolayers (A) but did not confer any ability to invade the HEp-2 cell monolayers (B).