Technical Abstract: Ciliates prey on bacteria in water and waste water systems. Compartmentalization of ingested material (including bacteria) in the food vacuoles of Tetrahymena and its egestion in the fecal pellet has been described and the survival of Salmonella enterica and E. coli O157:H7 in such fecal pellets has been reported. It is unclear whether the various pathotypes of E. coli interact with Tetrahymena in a fashion similar to that of the EHEC strain O157:H7. Using viability assays, we have obtained evidence that all six diarrheagenic pathotypes of E. coli not only evade digestion but remain viable and replicate within Tetrahymena fecal pellets. This suggests a possible role for Tetrahymena-E. coli interactions and more specifically for fecal pellets in the survival and dissemination of pathogenic E. coli in the environment. We observed by EM that the structure of the pellet sac is relatively fragile and allows for the escape of bacterial cells during multiplication. Also, the fecal pellets were sticky, as evidenced by their adherence into large flocs or to Tetrahymena cells. This adhesive property may play a role in the behavior of human pathogens in water systems because entrapment of bacterial prey in the adhesive floc may increase their occurrence in aquatic environments.