en Other Other Original Article Original Article <div style="text-align: justify;">Probiotic microorganisms have attracted a growing interest for prevention and therapy of gastrointestinal disorders. Many probiotic strains have been shown to inhibit growth and metabolic activity of enteropathogenic bacteria as well as their adhesion and invasion to intestinal cells. In the present study, we evaluated the interference of bacteria-free supernatants (BFS) of cultures belonging to sixteen strains of <em>lactobacilli </em>and <em>bifidobacteria</em>, with invasion of enteroinvasive <em>Escherichia coli</em> (EIEC) strain, by using human colonic adenocarcinoma cell lines, T84 and Caco2 cells.<em> To assess invasion of Caco-2 and T84 cells by EIEC, and measure the number of pathogens inside the enterocytes, the gentamicin protection assay was conducted. In addition, three different invasion inhibition assays were designed; namely </em><em>co-incubation, pre-incubation and treatment with the BFS of probiotics. Data obtained and theoretical calculation showed that the most effective assay in the prevention of pathogen invasion was treatment with BFS. Besides, co-incubation assay was more valid than pre-incubation assay in invasion prevention. The obtained results suggest that probiotics may produce some metabolites that strongly prevent invasion of enteroinvasive E.coli</em><em> into the small and large intestine. Also, probiotics are able to compete with or exclude pathogen</em> invasion.</div> Probiotics, enteroinvasive Escherichia coli, Caco-2 cells, T84 cells, adhesion 183 189 http://ijmcmed.org/browse.php?a_code=A-10-1241-1&slc_lang=en&sid=1 Zohreh Khodaii zkhodaii@yahoo.com 100319475328460010578 100319475328460010578 No Dietary supplements and Probiotic Research Center, Alborz University of Medical Sciences, Karaj, Iran. Sayyed Mohammad Hossein Ghaderian sghaderian@yahoo.co.uk 100319475328460010579 100319475328460010579 No Urogenital Stem Cell Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Mahboobeh Mehrabani Natanzi mmehrabani95@gmail.com 100319475328460010580 100319475328460010580 Yes Dietary supplements and Probiotic Research Center, Alborz University of Medical Sciences, Karaj, Iran.