International Journal for Biotechnology and Molecular Biology Research Vol. 1(4), pp. 47-57, July 2010 Available online http://www.academicjournals.org/IJBMBR ISSN 2141-2154 ©2010 Academic Journals Full Length Research Paper Patterns of colonization and immune response elicited from interactions between enteropathogenic bacteria, epithelial cells and probiotic fractions Mariana Carmen Chifiriuc 1 *, Coralia Bleotu 2 , Diana-Roxana Pelinescu 1 , Veronica Lazar 1 , Lia- Mara Ditu 1 , Tatiana Vassu 1 , Ileana Stoica 1 , Olguta Dracea 3 , Ionela Avram 1 and Elena Sasarman 1 1 Department of Microbiology, MICROGEN (Center for Research in Genetics, Microbiology and Biotechnology), Faculty of Biology, University of Bucharest, Ale. Portocalilor 1-3, Sector 5, 77206-Bucharest, Romania. 2 Institute of Virology Stefan S. Nicolau, 285 Mihai Bravu Ave. 030304, Bucharest, Romania. 3 Cantacuzino Institute, Sp. Independentei 103, Bucharest, Romania. Accepted 7 May, 2010 The purpose of this study was to investigate by in vitro studies the antimicrobial activity of eight lactic acid bacterial (LAB) strains belonging to Lactobacillus paracasei spp. paracasei, L. plantarum and L. rhamnosus species against Salmonella enteritidis, Shigella flexneri and EPEC pathogenic strains isolated from pediatric diarrhoea cases, simultaneously with the assessment of the cytotoxicity and immunomodulatory potential of the respective strains. The study of the adherence capacity to the cellular substrate represented by HeLa cells was performed by Cravioto’s adapted method. The cytotoxicity was determined on HeLa cells and the level of soluble pro- and anti-inflammatory cytokines was assessed by ELISA. Our in vitro studies are demonstrating that the selected probiotic strains are inhibiting the adherence and colonization of HeLa cells by the enteropathogenic strains isolated from pediatric diarrhoea mainly by direct competition for adherence sites, demonstrating their potential use in the treatment of pediatric gastro-intestinal disorders, as an alternative to/in association with antibiotics. A great advantage of the selected probiotic strains is their low cytotoxicity and ability to trigger a beneficial cytokine response in the epithelial cells, which potentiates their antimicrobial activity by stimulating the occurrence of a rapid immune response following the intestinal injury. Key words: Antimicrobial activity, immunomodulatory, cytokines, invasive bacteria, Lactobacillus, enteropathogenic bacteria, antimicrobial effect, cytotoxicity, probiotics. INTRODUCTION In recent years, several articles have reviewed the efficacy, mechanism of action, and safety of probiotics in the treatment of infectious disease (Vanderhoof and Young, 2002; Alvarez-Olmos and Oberhelman, 2001; Salminen and Arvilommi, 2001; Borriello et al., 2003; Ishibashi and Shoji, 2001). The term probiotic refers to a product or preparation *Corresponding author: E-mail: carmen_balotescu@yahoo.com. Abbreviations: LAB, Lactic acid bacterial; IL, interleukins; ATCC, american type culture collection; FCS, foetal calf serum; EPEC, Enteropathogenic E. coli. containing viable, defined microorganisms in numbers thought to be sufficient to alter the host's microbiota (by implantation or colonization) and thereby exert beneficial effects (Havenaar and Huis, 1992). The microorganisms most frequently used as probiotic agents are lactic acid bacteria (species of Lactobacillus, Enterococcus and Bifidobacterium) and nonpathogenic, antibiotic-resistant, ascosporic yeasts, especially Saccharomyces boulardii (FAO, 2001). Lactobacillus rhamnosus strain GG (ATCC 53103), which was originally isolated from human intestinal flora, is the most widely studied probiotic agent for adults and children (Gorbach, 2000). L. rhamnosus strain GG can prevent diarrhoea and atopic diseases among children (Szajewska and Mrukowicz, 2001; Kalliomaki et al., 2001; Majamaa and Isolauri, 1997). A