Elucidating the Effects of Physiological Factors on the Metabolic Profile of Lactobacillus Bacterial Isolates

Abstract

This study highlights the potential of Lactobacillus isolates (from curd & kefir) as probiotics against bowel infections. The isolates showed optimal growth at 0.5% salt concentration and pH 5, with varying levels of tolerance to different salt concentrations and pH levels. Notably, S12 and S33 exhibited high colony counts at 0.5% salt concentration, indicating their potential as salt-tolerant isolates. Lactobacillus species can strengthen the gut barrier, produce antimicrobial substances, and modulate the immune system, contributing to their potential health benefits. These findings suggest that these isolates could be used to develop novel probiotics or antimicrobial therapies to prevent or treat bowel infections, and further research is needed to explore their mechanisms of action and potential applications.

Introduction

I. Overview

• Probiotics support gut health by regulating the microbiome, strengthening gut barriers, boosting immunity, and reducing inflammation.

• Lactobacillus spp., found in fermented foods like curd and kefir, are known for:

  • Producing beneficial compounds (lactic acid, hydrogen peroxide, bacteriocins)

  • Enhancing gut immunity and inhibiting pathogens

  • Modulating metabolism and synthesizing vitamins like biotin and K

II. Study Objective

To isolate, characterize, and evaluate Lactobacillus strains from traditional dairy products for:

• Environmental tolerance (salinity, pH, temperature)

• Antimicrobial activity against common gut pathogens

III. Methodology

1. Isolation & Identification

   • Samples from curd and kefir plated on MRS agar, incubated anaerobically.

   • Colonies identified via Gram staining.

2. Biochemical & Physiochemical Analysis

   • Tested for carbohydrate fermentation, salt and pH tolerance.

   • Optical density (OD at 620 nm) used to assess bacterial growth.

3. Environmental Tolerance Tests

   • Salinity: Cultures grown in 0.5%, 0.8%, and 1% NaCl.

   • pH: Cultures grown at pH 3, 4, and 5.

   • Temperature: Metabolites incubated at 25°C, 50°C, 75°C, and 100°C to activate antimicrobial properties.

4. Antimicrobial Testing

   • Bacterial metabolites tested against Salmonella Typhimurium and Staphylococcus aureus using disc diffusion on Muller-Hinton agar.

IV. Results & Discussion

1. Salinity Tolerance

• Isolates S12 and S33 showed optimal growth at 0.5% NaCl, suggesting good salt tolerance.

2. pH Tolerance

• Best bacterial growth observed at pH 5, particularly by isolates S12 and 3, showing good acid tolerance relevant to gut conditions.

3. Antimicrobial Activity

• Metabolites from S12 and S33 displayed strong inhibition against both Salmonella and Staphylococcus.

• S12 showed especially strong effects, indicating potential therapeutic relevance.

• Highest activity observed when metabolites were activated at 75°C, emphasizing the temperature-dependent nature of bioactivity.

Conclusion

The bacterial isolates S12 and S33 demonstrated exceptional physiological robustness, showcasing optimal growth at 0.5% salt concentration, with S12 and S33 exhibiting the highest colony counts, indicating their potential as salt-tolerant isolates. Additionally, they displayed good tolerance to varying pH levels, with optimal growth at pH 5, and some ability to grow well at pH 4. Notably, these isolates maintained their antimicrobial activity, particularly against Salmonella Typhi and Staphylococcus aureus, with S12 displaying excellent results, and their effectiveness was significantly enhanced at a temperature of 75°C. The combination of salt tolerance, pH resilience, and temperature stability in S12 and S33 underscores their potential as probiotic candidates with industrial applicability, highlighting their ability to withstand diverse environmental conditions while retaining metabolic and antimicrobial functionality. The metabolic profile of Lactobacillus isolates is significantly influenced by physiological factors. Strains demonstrating resilience to varied pH, bile salts, and temperature shifts maintained metabolic and antimicrobial functionality. These findings underscore the importance of physiological robustness in probiotic efficacy and industrial applicability.

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Copyright

Copyright © 2025 Rinisha Peter, Shadma Siddqui . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.