Exploring the Antibacterial Potency of Bacteriocins

Abstract

Background: Increasing antibiotic resistance has intensified the search for alternative antimicrobial agents. Bacteriocins are ribosomally synthesized antimicrobial peptides that can exhibit targeted inhibitory activity against bacteria. Objective: To assess and compare the in vitro antibacterial activity of bacteriocin extracts obtained from four Lactobacillus isolates, designated IS1, IS2, IS4, and IS6, against Salmonella typhi, Bacillus subtilis, and Streptococcus mutans. Methods: Extracts from the four isolates were evaluated using broth microdilution and microbial growth inhibition assays. Optical density measurements and inhibitory activity were assessed using a ProMax5 ELISA microplate reader (USA). Minimum inhibitory concentration (MIC) and half-maximal inhibitory concentration (IC50) values were compiled for each isolate–test organism combination. Results and conclusion: The Lactobacillus-derived extracts exhibited isolate-dependent activity against the tested Gram-positive and Gram-negative organisms. Numerical MIC and IC50 values were reported for all four isolates against B. subtilis and S. mutans, whereas the values for IS1 against S. typhi were recorded as NA. The findings support further investigation of these extracts as potential antibacterial agents; confirmation of the reported concentration values and additional characterization are necessary before therapeutic applications can be established.

Introduction

The study investigates the antibacterial potential of bacteriocin extracts produced by different Lactobacillus isolates as possible alternatives or complements to conventional antibiotics in response to the growing problem of antibiotic resistance. Bacteriocins are ribosomally synthesised antimicrobial peptides that can inhibit susceptible bacterial strains, making them promising candidates for developing targeted antimicrobial strategies.

The research focuses on four Lactobacillus isolates, designated IS1, IS2, IS4 and IS6, to evaluate their inhibitory activity against three bacterial pathogens: Salmonella typhi, Bacillus subtilis and Streptococcus mutans. The study employed in vitro antibacterial assays and broth microdilution techniques to determine the Minimum Inhibitory Concentration (MIC) and IC50 values. A ProMax5 ELISA microplate reader was used to measure bacterial growth inhibition. Different culture media, including MRS broth, nutrient broth and Mueller–Hinton agar, were used during the experimental procedures.

Major findings

1. Activity against Salmonella typhi: IS4 and IS6 demonstrated comparatively stronger inhibitory activity, with MIC values of 0.05 and 0.055, respectively. Their IC50 values were 0.047 and 0.039. IS1 showed no reported activity (NA).

2. Activity against Bacillus subtilis: All four isolates demonstrated reported inhibitory activity. IS1 recorded the lowest MIC value (0.109), while IS6 showed the lowest IC50 value (0.118).

3. Activity against Streptococcus mutans: IS4 demonstrated the lowest MIC value (0.128), followed closely by IS6 (0.132). IS1 recorded the highest MIC value (0.52), although its reported IC50 was 0.058.

Conclusion

The reported MIC and IC50 values suggest that extracts from Lactobacillus isolates IS1, IS2, IS4, and IS6 exhibit different inhibitory profiles against S. typhi, B. subtilis, and S. mutans. Responses against S. typhi varied among isolates. Numerical endpoints were reported for every isolate against B. subtilis, while the S. mutans results showed substantial variation in MIC values. These findings support consideration of isolate-specific responses when investigating bacteriocins as antimicrobial agents.

References

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Copyright

Copyright © 2026 Archana Patil, Virendra Kumar. 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.