In Vitro CHARACTERIZATION OF GUT STRESS TOLERANT POTENTIAL PROBIOTIC Lactobacillus spp. ISOLATED FROM TRADITIONAL CURDS

One of the most prevalent probiotics in fermented dairy products, mostly in curds, is Lactobacillus. However, not all Lactobacillus species can endure the stressors of the human gut, such as the stomach's low pH and the liver's bile secretion into the small intestine. Therefore, the objective of the present study was to isolate, identify, and test the potential probiotic Lactobacillus species from curds collected from ten different dairy shops in Khulna city. From ten samples, bacteria of 5 samples could survive the usual human bile salt content (0.7%) and stomach acidity (pH 2.0) and were marked as 5 isolates (S1, S2, S3, S4, S5). They were selected for morphological and 10 biochemical tests (indole test, catalase test, motility test, methyl red test, Voges–Proskauer test, citrate utilization test, urease test, casein digestion test, oxidase test, triple sugar iron agar test). All bacterial isolates were tested for probiotic traits such as acid, salt, and phenol stress survivability, multiple sugars and lactose fermentation, and proteolytic activity. MRS broth acid tolerance tests were performed at pH 2, 3, 4, 5, 6, 7, and 8. All isolates survived under very acidic conditions (pH 2.0) as well as in an alkaline medium (pH 8.0). Salt tolerance was tested in MRS broth with 2%, 4%, and 8% NaCl concentrations. Every isolate survived in 2% and 4% NaCl. Phenol tolerance was tested in MRS broth with 0.2%, 0.3%, and 0.4% phenol concentrations. All strains survived in 0.2% and 0.3% phenol. All isolates fermented 10 of 12 sugars. All isolates were susceptible to 13 of 15 antibiotics, indicating a probiotic-enriched diet following antibiotic treatment. This study found that curd-isolated gut stress-tolerant Lactobacillus species are potential probiotics, with S1 and S2 isolates performing the best. Further research is needed on the isolates' strains and how to employ them in probiotic-enriched meals.

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