Folia Microbiol. 54 (2), 157–160 (2009) http://www.biomed.cas.cz/mbu/folia/ Live and Heat-Inactivated Lactobacilli from Feces Inhibit Salmonella typhi and Escherichia coli Adherence to Caco-2 Cells S.N. OSTAD a , A.A. SALARIAN a , M.H. GHAHRAMANI a , M.R. FAZELI b , N. SAMADI b , H. JAMALIFAR b a Department of Toxicology–Pharmacology, Faculty of Pharmacy and Pharmaceutical Sciences Research Center, Tehran University of Medical Sciences, 14155/6451 Tehran, Iran fax +98 21 6646 1178 e-mail ostadnas@sina.tums.ac.ir b Department of Drug and Food Control, Faculty of Pharmacy, Tehran University of Medical Sciences, 14155/6451 Tehran, Iran Received 28 April 2008 Revised version 6 January 2009 ABSTRACT. A quantitative approach has been proposed to evaluate the competitive inhibition of Escheri- chia coli and Salmonella typhi by live and heat-inactivated laboratory isolated Lactobacillus sp. on adhesion to monolayer of Caco-2 cells. Three species of Lactobacillus (L. casei, L. acidophilus, L. agilis) isolated from human neonate feces and two commercial probiotic strains (L. casei, L. acidophilus) have been compa- red for probiotic activity. All lactobacilli were able to attach to the Caco-2 cells, however, the degree of adhe- sion was bacterial strain-dependent. The adhesion indices of the two commercial probiotic strains were not significantly different from the values obtained for the other two similar fecal strains (p > 0.01). The inhibit- ion of attachment of the pathogenic bacteria by inactivated cells of fecal L. acidophilus was examined and com- pared to the results of live bacteria. The inhibition pattern was similar for live and heat-inactivated L. acido- philus (p > 0.01). The number of attached pathogenic bacteria to the Caco-2 cells decreased when the number of L. acidophilus increased from 10 6 to 10 9 CFU/mL. The heat-inactivated L. acidophilus displayed similar probiotic activity compared to the live bacteria. Abbreviations CFU colony forming unit MRS broth Man–Rogosa–Sharp broth SCDB soybean–casein digest broth EMB agar eosin–methylene blue agar PBS phosphate-buffered saline SS agar Salmonella–Shigella agar Probiotics are defined as live microorganisms which, when administered in adequate amounts, bene- ficially affect the health of the host (Fuller 1989; Salminen et al. 1999; Klaenhammer 2000; FAO/WHO 2001). Most of the probiotic bacteria are lactic acid bacteria which are useful in the treatment of dysfunctions that disturb intestinal microflora and abnormal gut permeability (Lee and Salminen 1995; Ebringer et al. 2008; Koninkx and Malago 2008; Rigon-Zimmer et al. 2008). Successful probiotic bacteria are usually able to colo- nize the intestine, at least temporarily, by adhering to the intestinal mucosa. It is also suggested that adhesive probiotic bacteria could prevent the attachment of pathogens, such as pathogenic coliform bacteria and clos- tridia and stimulate their removal from the infected intestinal tract (Tamura et al. 1983; Lidbeck et al. 1987; Benno and Mitsuoka 1992; Saxelin et al. 1995). They could inhibit pathogenic microbial growth by product- ion of inhibitory compounds, such as organic acids, dihydrogen peroxide and bacteriocins (Juven et al. 1992; Fazeli et al. 2004, 2006; Walencka et al. 2008). Adhesion of probiotic microorganisms to the intestinal mu- cosa is considered important for many of the observed probiotic health effects such as antagonistic activity against enteropathogens (Coconnier et al. 1993a), modulation of immune system (Schiffrin et al. 1997) and increased healing of damaged gastric mucosa (Elliot et al. 1998). Therefore, adhesion is one of the main selection criteria for probiotic microorganisms. It was reported that orally administered nonviable probiotics are less effective in modulating the immune system than viable probiotics due to their lower ability to bind to the intestinal mucosa (Perdigon et al. 1995; Kato et al. 1994), suggesting that probiotics should be viable in order to elicit beneficial health effects. However literature overview indicates that although viable probiotics have more documented health effects than nonviable probiotics, the latter are not without effect (Ouwehand and Salminen 1998; Čepeljnik et al. 2007). Therefore, we proposed to evaluate the adhesion of fecal lactobacilli to cultured Caco-2 cells. Furthermore, the probiotic activity of heat-inactivated lactobacilli has been compared with the results of the same live strain.