A microbiological survey of the human gastric ecosystem in the search of strains with probiotic potential

Abstract

[Introduction] The human stomach seems to harbour a greater microbial diversity that that anticipated. Among the colonizing microorganisms, different lactic acid bacteria belonging mainly to the genera Lactobacillus and Streptococcus are present. These bacteria might be playing important roles in the maintenance of the healthy status of the host. Additionally, they could be used in the design of probiotic to counteract pathogens such as Helicobacter pylori.

[Objectives] A microbiological study of biopsia samples from the gastric mucosa of healthy individuals was carried out by culturing and a metagenomic approach in order to search for lactic acid bacteria with desirable probiotic traits.

[Methods] Twelve biopsies of stomach were analyzed by culturing. Of these, DNA from four samples was amplified with universal bacterial primers and the amplicons pyrosequenced. Gastric lactobacilli isolates were characterized by a variety of in vitro assays which included, among others, production of antimicrobial compounds, antioxidative activity, acid resistance and ability to adhere to a gastric cell line.

[Results] Occurrence of lactobacilli was evidenced by both culturing and pyrosequencing. Ten strains belonging to the species Lactobacillus gasseri (3), L. reuteri (2), L. vaginalis (2), L. fermentum (2), and L. casei (1) species were selected for further characterization. Strains showed good tolerance and survival to low pH and were all shown to be free of atypical antibiotic resistances. Species and strain specific differences in the production of H2O2, inhibition of Helicobacter pylori and adhesion to the gastric epithelium were encountered.

[Conclusions] The presence of alive members of the genus Lactobacillus in the human stomach of healthy people was confirmed. A set of gastric lactobacilli was extensively characterized. Some strains showed beneficial properties, thus constituting good probiotic candidates.