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Preliminary in vitro screening of gut isolates tentatively identified as Lactobacillus delbrueckii VR1 and Bacillus subtilis VR2 from Nile tilapia (Oreochromis niloticus) as potential probiotic candidates
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S. Vijayaram *   , R. Thirumurugan , M. Gobi , R. Kirubakaran |
| Department of Biotechnology, Karpagam Academy of Education, Coimbatore-641021, Tamil Nadu, India |
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Abstract: (10 Views) |
We recovered two culturable isolates from pooled gut samples of three Nile tilapia (Oreochromis niloticus) collected in the Kaveri River, Tamil Nadu, India, on de Man, Rogosa and Sharpe (MRS) agar. They were tentatively identified as Lactobacillus delbrueckii VR1 and Bacillus subtilis VR2 (about 3.2 × 10⁶ and 1.8 × 10⁶ colony-forming units (CFU) g⁻¹ of gut content, respectively), based on 16S rRNA gene sequencing results. Neither isolate showed clear haemolysis. Turbidity (optical density at 600 nm, OD₆₀₀) after 3 h under acid, bile salt, NaCl and temperature challenge differed between the isolates and among conditions, but because these were single-endpoint readings made without viable counts they are reported as OD responses and not as growth, survival or tolerance. Auto-aggregation was low (6.8–11.9% for VR1 and 5.4–12.5% for VR2 after 1–3 h), whereas mixed cultures with four pathogens gave co-aggregation values of 49.7–62.5%, compared with 6.8–14.2% in the single-culture controls. Solvent-affinity values (47.8–76.5%) were obtained from an assay adapted from microbial adhesion to hydrocarbons/solvents (MATH/MATS) that used polar solvents and are not classical hydrophobicity values. Cell-free supernatants inhibited all six pathogens tested (zones of 7.8–14.1 mm, and 1.7–4.0 mm smaller after adjustment to pH 7); both isolates showed lipase and amylase activity on plates, and radical-scavenging activity in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was about 46% (VR1) and 51% (VR2), compared with 67.9% for ascorbic acid. These findings describe in vitro functional characteristics only. Genome-based identification, antimicrobial-resistance and virulence screening, and controlled feeding trials in Nile tilapia are needed before any probiotic efficacy or safety can be claimed.
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| Keywords: Aquaculture, Probiotic candidate, Cell surface properties, Antimicrobial activity, Tentative identification, 16S rRNA gene |
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Full-Text [PDF 1010 kb]
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Type of Study: Research |
Subject:
General
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