Open Access Highly Accessed Research article

Functional characterization of probiotic surface layer protein-carrying Lactobacillus amylovorus strains

Ulla Hynönen1, Ravi Kant1, Tanja Lähteinen1, Taija E Pietilä1, Jasna Beganović2, Hauke Smidt3, Ksenija Uroić2, Silja Åvall-Jääskeläinen1 and Airi Palva1*

Author Affiliations

1 Department of Veterinary Biosciences, Division of Microbiology and Epidemiology, University of Helsinki, P.O. Box 66, Helsinki 00014, Finland

2 Faculty of Food Technology and Biotechnology, Laboratory of Antibiotic, Enzyme, Probiotic and Starter Culture Technologies, University of Zagreb, Pierottijeva 6, Zagreb 10000, Croatia

3 Laboratory of Microbiology, Wageningen University, Dreijenplein 10, Wageningen NL-6703 HB, The Netherlands

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BMC Microbiology 2014, 14:199  doi:10.1186/1471-2180-14-199

Published: 28 July 2014

Abstract

Background

Adhesiveness to intestinal epithelium, beneficial immunomodulating effects and the production of pathogen-inhibitory compounds are generally considered as beneficial characteristics of probiotic organisms. We showed the potential health-promoting properties and the mechanisms of probiotic action of seven swine intestinal Lactobacillus amylovorus isolates plus the type strain (DSM 20531T) by investigating their adherence to porcine intestinal epithelial cells (IPEC-1) and mucus as well as the capacities of the strains to i) inhibit the adherence of Escherichia coli to IPEC-1 cells, ii) to produce soluble inhibitors against intestinal pathogens and iii) to induce immune signaling in dendritic cells (DCs). Moreover, the role of the L. amylovorus surface (S) –layers - symmetric, porous arrays of identical protein subunits present as the outermost layer of the cell envelope - in adherence to IPEC-1 cells was assessed using a novel approach which utilized purified cell wall fragments of the strains as carriers for the recombinantly produced S-layer proteins.

Results

Three of the L. amylovorus strains studied adhered to IPEC-1 cells, while four strains inhibited the adherence of E. coli, indicating additional mechanisms other than competition for binding sites being involved in the inhibition. None of the strains bound to porcine mucus. The culture supernatants of all of the strains exerted inhibitory effects on the growth of E. coli, Salmonella, Listeria and Yersinia, and a variable, strain-dependent induction was observed of both pro- and anti-inflammatory cytokines in human DCs. L. amylovorus DSM 16698 was shown to carry two S-layer-like proteins on its surface in addition to the major S-layer protein SlpA. In contrast to expectations, none of the major S-layer proteins of the IPEC-1 -adhering strains mediated bacterial adherence.

Conclusions

We demonstrated adhesive and significant pathogen inhibitory efficacies among the swine intestinal L. amylovorus strains studied, pointing to their potential use as probiotic feed supplements, but no independent role could be demonstrated for the major S-layer proteins in adherence to epithelial cells. The results indicate that many intestinal bacteria may coexist with and confer benefits to the host by mechanisms not attributable to adhesion to epithelial cells or mucus.

Keywords:
S-layer; Lactobacillus; Adhesion; IPEC-1; Dendritic cell