Isolation and Preliminary Characterization of Probiotic Isolates from Healthy Thai Adult Feces

Abstract

Probiotics are known for health-promoting microorganisms, for examples, assisting gastrointestinal digestion and short chain fatty acid producers. Several current oral human probiotics were derived from human samples; yet, of various ethnic (genetics) and dietary patterns. As probiotics from similar ethnic (genetics) and dietary pattern might confer certain advantages (e.g., more compatibility with hosts), this study isolated and characterized probiotics from healthy Thai adults. To screen for potential probiotic isolates from healthy Thai adult feces, and preliminary characterize these probiotic isolates by biochemical tests and 16S rRNA gene sequencing, following the established Thailand’s Food and Drug Administration (FDA) and National Center for Genetic Engineering and Biotechnology (BIOTEC) guidelines. Twenty fecal samples with clinically verified healthy Thai males and females aged 22-42 years were cultivated on MRS (or M17) media along the broad probiotic screenings (pH 4.0 and 0.1% oxgall) for bacterial probiotic propagation. All derived colonies of different morphologies were continued colony PCR using universal probiotic primers (specific for genera Bifidobacterium, Enterococcus, Lactobacillus, Pediococcus and Streptococcus thermophilus), and only PCR-positive colonies from any of these probiotic primer pair were further cultivation for isolates. Then, these isolates were screened and characterized general probiotic properties that included acid tolerance (pH 2.0), bile salt tolerance (0.3% bile salt), hydrophobicity, antibiotic (ampicillin, ciprofloxacin, erythromycin and vancomycin) susceptibility, no hemolysis activity, catalase, and potassium hydroxide (KOH). The final passing isolates represented potential probiotic isolates that could perhaps maintain in gastrointestinal tract with safety, and were full-length 16S rRNA gene sequenced to identify the genus and species by BLASTN against non-redundant GenBank database. A total of 295 bacterial isolates were obtained from the cultivated on MRS (or M17) media along the broad probiotic screenings from 20 fecal samples. Then, following the general probiotic property characterizations and the full-length 16S rRNA gene sequence analysis, 7 potential isolates were finally derived: 2 Bifidobacterium animalis subsp. lactis, 1 Lactobacillus (new genus name as Limosilactobacillus) reuteri, 1 L. reuteri or L. vaginalis, and 3 Pediococcus pentosaceus. These isolates exhibited strong acid and bile salt tolerances, and relatively high cell surface hydrophobicity. These isolates were susceptible to ampicillin and erythromycin, similar to a reference probiotic control Lactobacillus casei strain Shirota; and the CU13-450 and CU13-451 were also susceptible to vancomycin, similar to a reference control Bifidobacterium breve. Catalase-negative consistent with these bacteria in intestinal tract as anaerobes or facultative anaerobes, and KOH-negative result inferred the Gram-positive bacteria consistent with the full-length 16S rRNA gene sequence identification (Bifidobacterium, Lactobacillus, and Pediococcus are Gram-positive bacteria). No hemolysis activity was observed for these isolates. These 7 probiotic isolates had general probiotic properties and with confirmed the 16S rRNA gene sequences, that follow the Thailand’s FDA and BIOTEC guidelines. However, additional beneficial function investigations, such as in vitro epithelial cell adhesion and in vivo animal model, and whole genome sequencing, should be performed to better validate their possible human health benefits and safety.