Exploring Dairy-Derived Probiotics: Microbiological, Biochemical and Functional Profiling of Indigenous Lactic Acid Bacteria Isolates

Lactic acid bacteria (LAB) derived from indigenous dairy sources represent a valuable and largely untapped reservoir for the development of safe, effective, and cost-efficient probiotic formulations. The present study aimed to isolate, characterize, and functionally evaluate LAB from fresh and fermented milk samples obtained from local dairy producers in Lucknow, Uttar Pradesh, India. Using selective media — de Man, Rogosa and Sharpe (MRS) agar, milk agar, and M17 agar — five phenotypically distinct isolates designated M1 through M5 were recovered and subjected to a comprehensive battery of morphological, physiological, biochemical, and functional tests. All five isolates were confirmed as Gram-positive, catalase-negative, non-spore-forming organisms consistent with the defining characteristics of LAB. Bacilli-shaped isolates (M1–M3) were provisionally identified as belonging to the Lactobacillus group, while cocci-shaped isolates (M4–M5) were consistent with Lactococcus or Leuconostoc genera. Biochemical profiling revealed differential patterns of carbohydrate fermentation, citrate utilization, and exopolysaccharide (EPS) production ranging from 95.3 mg/L (M5) to 117.3 mg/L (M2). Probiotic functional assessment demonstrated that M1, M2, and M3 exhibited robust tolerance to simulated gastric acid stress (pH 3.0, 2 h) and bile salt concentrations of 0.3%, both critical determinants of gastrointestinal survivability. Haemolytic activity testing confirmed the absence of beta-haemolysis in all isolates, indicating a favourable safety profile. Antibiotic susceptibility profiling showed general sensitivity to erythromycin, clindamycin, cephalothin, and oxytetracycline, with intrinsic resistance to ofloxacin and co-trimoxazole — a resistance pattern characteristic of and acceptable in probiotic LAB. Collectively, isolates M1, M2, and M3, with M3 being most promising overall, meet the key criteria for probiotic candidacy. These findings advocate for systematic exploitation of indigenous dairy microbiota as sustainable platforms for next-generation probiotic innovations.

Dairy probiotics, exopolysaccharides, antibiotic susceptibility, Lactobacillus

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