Enteroaggregative Escherichia coli (EAEC) strains enter and survive within cultured intestinal epithelial cells

Enteroaggregative Escherichia coli (EAEC) is an emerging pathogen associated to cases of acute or persistent diarrhea in children and adults from developed and developing countries. These microorganisms also have been isolated from human immunodeficiency virus-infected patients. EAEC exhibits aggregative adherence (AA) in HEp-2 cells. This pattern is characterized by the production of bacteria aggregates adhered to monolayer cultured cells with a "stacked brick" phenotype. The AA pattern is related to the presence of a 60MDa plasmid (pAA). In the present study, we evaluated the adherence, invasion and persistent survival of five EAEC strains with Caco-2 and T84 cells, by a bacteria invasion assay and transmission electron microscopy. EAEC isolated from cases of acute infantile diarrhea can be internalized by intestinal epithelial cells cultivated in vitro, suggesting that these strains may employ a mechanism of host cell invasion to colonize the intestinal mucosa. Results showed that EAEC strains could survive intracellularly up to 72h. Our data support evidence that EAEC is able to invade, persist and replicate within intestinal cells for extended time. This strategy may be advantageous to EAEC in colonization and survival, favoring the exploitation of an intracellular niche where these strains are protected against host clearance mechanisms, immune system and antibiotic treatment. Intracellular persistence of EAEC may be associated with development of persistent diarrhea associated to these microorganisms. To our knowledge, this is the first report of EAEC intracellular survival in cultured intestinal epithelial cells.