Uncovering Novel Antimicrobial-Producing Microorganisms in Soil Environments

The microbial diversity of soil environments offers a promising source of potential solutions in the face of antimicrobial resistance, which, nowadays, is viewed as a significant threat to global health. This research centres on isolating and screening lactic acid bacteria (LAB) from diverse soil samples (n=5), a promising reservoir of beneficial traits for food and medical industry applications. Furthermore, soil samples were serially diluted and 0.1 and 1 mL of inoculum were plated in duplicate onto de Man Rogosa Sharpe (MRS), Plate Count Agar (PCA), Violet Red Bile Glucose Agar (VRBGA), and Sabouraud Dextrose Agar (SDA) for the identification and enumeration of LAB, total viable counts, Enterobacterales, and yeasts and molds, respectively. Plates were incubated at their corresponding temperature in aerobiosis and anaerobiosis conditions. Colony counts indicated total bacterial loads exceeding 10⁵ CFU/g, while lactic acid bacteria (LAB) ranged between 10² and 10³ CFU/g. All samples except P3 exhibited elevated levels of Enterobacterales at approximately 10² CFU/g.

Functional screening of 79 LAB isolates was conducted to evaluate their antagonistic activity against pathogenic strains, including S. aureus ATCC25923, Klebsiella oxytoca ATCC49131, and Escherichia coli ATCC25922 using the spot-on-lawn method, showing inhibition rates of 50.63%, 40.50%, and 45.56%, respectively. Lactococcus lactis ATCC11454 and Lactobacillus reuteri DSM17938 were included in each assay to assess the bacteriogenic potential of LAB isolates with standard controls. This research highlights soil environments as promising sources of potential antimicrobials, with applications in food science and the potential to address antimicrobial resistance in future medical practices.