Identification of potential probiotic cultures from the Samara region soils

BACKGROUND: Probiotics exert diverse beneficial effects on the human body; probiotic preparations restore the normobiota of the gastrointestinal mucosa and exhibit immunomodulatory properties. Dairy products are the most extensively studied sources of probiotic cultures. Recently, however, active efforts have been directed toward the search for probiotic strains. Soil, as an ecosystem with the greatest microbial biodiversity, represents a promising source.

AIM: This work aimed to analyze the diversity of microorganism species in soils of the Samara Region and to describe the main groups of potentially probiotic microorganisms.

METHODS: A microbiological assessment of agricultural soils was performed. A total of 75 soil samples were collected. The following culture media were used for bacteriological analysis: universal chromogenic agar, Mueller–Hinton agar supplemented with 5% sheep blood, Middlebrook agar, Rogosa agar, mannitol salt agar, agar for isolation of Brucella spp., agar for isolation of the Burkholderia cepacian complex, xylose lysine deoxycholate agar, cetrimide agar, Ashby glucose agar, agar for isolation of Clostridium spp., anaerobic agar, Reddy differential agar, Sabouraud agar, and granulated Czapek–Dox agar. Samples were plated using the Drigalski method. Microbial colonies were identified by MALDI-TOF mass spectrometry using a Microflex LT instrument.

RESULTS: In all soil samples, major representatives of microorganisms typically inhabiting the human gastrointestinal tract and used as probiotics were detected: Bacillus, Bifidobacterium, Enterococcus, Lactobacillus, Ligilactobacillus, and Streptococcus. Forty-five Bacillus species were identified. Among Lactobacillus species, L. jenseni and L. sakei were most frequently detected (in 50.7% of samples), followed by L. plantarum (46.7%). Ligilactobacillus agilis was the most frequently detected species (32% of samples); another important probiotic microorganism, Lig. salivarius, was isolated in 24% of samples. Enterococcus faecium was detected in 68% of samples. Although Streptococcus species are not typical representatives of the human gastrointestinal microbiota, Str. salivarius, identified in 4% of samples, is a dominant component of the normal oral microbiota throughout human life.

CONCLUSION: The obtained data indicate that microorganisms identified in soil samples may be used for the development of new probiotic preparations. Most of these microorganisms (Bacillus, Bifidobacterium, Enterococcus, Lactobacillus, Ligilactobacillus) are already applied in clinical practice for the treatment of gastrointestinal diseases.