en Host-pathogen interactions and susceptibility factors Host-pathogen interactions and susceptibility factors Original article Original article <strong>Introduction: </strong>The strain-specific capabilities of lactobacilli are critical for gut colonization. In this study, we evaluated various colonization determinants of 42 fecal <em>Lactobacillus plantarum</em> isolates from the healthy human fecal samples. <strong>Methods:</strong> We investigated the attachment to the Caco-2 cell line, biofilm formation ability and cell surface activity of the isolates. Such properties were comparatively studied, and the regression between these features was statistically analyzed. <strong>Results:</strong> Among our results 18 (42.9%) were non-adhesive, 11 (26.2%) moderate adhesive and 13 (31%) strongly adhesive. The results showed that some isolates were significantly capable of biofilm formation. The highest rate of auto-aggregation was recorded for <em>L. plantarum</em> isolate RPR 240 (58%).<strong> Conclusion:</strong> Our results revealed a high degree of variability among colonization characteristics of the <em>L. plantarum</em> isolates indicating strain-specificity. Also, the colonization properties of the potential probiotic isolates had no significant correlation with each other. Our results confirmed the necessity of further <em>in vivo</em> colonization assays for selection of probiotic candidates. Probiotics, Strain specificity, Colonization ability, Caco-2 cell, Cell surface activity 13 19 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-104-1&slc_lang=en&sid=1 Mahdi Rohani kia.rohani@gmail.com 0000-0001-8956-5072 Yes Department of Microbiology, Pasteur Institute of Iran, Tehran, Iran Moslem Papizadeh moslempapizadeh@yahoo.com 0000-0002-0966-1951 No Department of Microbiology, Pasteur Institute of Iran, Tehran, Iran Mohammad Reza Pourshafie pour62@yahoo.com 0000-0002-6226-7064 No Department of Microbiology, Pasteur Institute of Iran, Tehran, Iran