# Evaluation of the antimicrobial properties of potential probiotic lactic acid bacteria from raw and fermented cow milk

## TL;DR

This study evaluates lactic acid bacteria from raw and fermented cow milk in Ethiopia for their potential as probiotics, based on their antimicrobial properties and survival under gastrointestinal conditions.

## Contribution

The study identifies and characterizes lactic acid bacteria from Ethiopian cow milk with potential probiotic properties, including antimicrobial activity and gastrointestinal tolerance.

## Key findings

- Isolates showed resistance to vancomycin and gentamicin but susceptibility to bacitracin, ampicillin, tetracycline, and penicillin.
- Antimicrobial activity was observed against S. aureus, E. coli, P. aeruginosa, and S. Typhi.
- Lactic acid production ranged from 5.0% to 8.2%, with some isolates coagulating milk within 12 hours.

## Abstract

Lactic acid bacteria (LAB) comprise a diverse group of Gram-positive, non-spore-forming, non-motile, catalase-negative microorganisms that produce lactic acid as a major fermentation end product and are commonly associated with fermented foods. The aim of this study was to isolate, characterize, and evaluate lactic acid bacteria from fermented and raw cow milk as potential probiotic candidates. Twenty-five raw and fermented cow milk samples collected from South and North Gondar, Ethiopia, were analyzed, yielding twenty presumptive LAB isolates. Isolation was performed using de Man, Rogosa, and Sharpe (MRS) agar. Isolates were characterized using morphological and biochemical tests and evaluated for tolerance to conditions simulating the gastrointestinal environment, including variations in pH, sodium chloride concentration, and temperature. Antimicrobial activity of cell-free supernatants was assessed using the agar well diffusion method against selected Gram-positive and Gram-negative pathogenic bacteria. All isolates exhibited γ-hemolysis (non-hemolytic activity). The isolates showed resistance to vancomycin and gentamicin, while susceptibility was observed to bacitracin, ampicillin, tetracycline, and penicillin. Lactic acid production ranged from 5.0% to 8.2%, and several isolates induced milk coagulation within 12 h. Antimicrobial assays demonstrated inhibitory activity against Staphylococcus aureus (15–27 mm), Escherichia coli (8–13 mm), Pseudomonas aeruginosa (10–17 mm), and Salmonella Typhi (8–14 mm). The LAB isolates exhibited several in vitro functional properties consistent with potential probiotic candidates from raw and fermented cow milk. However, species-level identification and safety assessment remain presumptive, and further molecular characterization as well as comprehensive in vitro and in vivo studies are required to confirm their probiotic potential and suitability for industrial application.