Citizen Contribution for Searching for Alternative Antimicrobial Activity Substances in Soil

Abstract

Antimicrobial resistance (AMR) is problematic worldwide, and due to the loss of efficiency of many antibiotics, the pressure to discover alternative antimicrobial molecules has increased. Soil harbors a great biodiversity and biomass of microorganisms, and many antibiotics are produced by soil microbiota. Therefore, soil is a promising reservoir to find new antimicrobial agents. In this respect, novel pedagogical strategies regarding the AMR global crisis have recently been developed in different countries worldwide. Highlighted is the service-learning project “MicroMundo” integrated in a global Citizen Science project called “Tiny Earth”. Hence, the present work aimed at determining the antimicrobial activity of soil bacteria, the biodiversity of the selected isolates as putative antimicrobial producers, and their antibiotic resistance profile. Moreover, through the MicroMundo project, we tried to illustrate the relevant link between science and education and the benefits of implementing service-learning methodologies to raise awareness of the AMR problem and to contribute to the search for new alternatives. A total of 16 teachers, 25 university students and 300 secondary school students participated in the search for antimicrobial activity on a collection of 2600 isolates obtained from a total of 130 soil samples analysed. In total, 132 isolates (5% of total tested) were selected as potential antimicrobial producers when two indicator bacteria were used (Escherichia coli and Staphylococcus epidermidis); the most frequent genus among these isolates was Bacillus, followed by Pseudomonas, Paenibacillus and Serratia. The antimicrobial activity (AA) of the 132 potential antimicrobial producers was studied in a second step against 15 indicator bacteria (of six genera and thirteen species, including relevant pathogens). Of the 132 potentially producing bacteria, 32 were selected for further characterization. In this respect, 18 isolates showed low AA, 12 isolates were considered as medium producers, and 2 highly antimicrobial-producing isolates were found (Brevibacillus laterosporus X7262 and Staphylococcus hominis X7276) showing AA against 80% of the 15 indicators tested. Moreover, 48% of the antimicrobial-producing bacteria were susceptible to all antibiotics tested. Due to citizen science, antimicrobial-producing bacteria of great interest have been isolated, managing to raise awareness about the problem of AMR.

Searching for Antimicrobial-Producing Bacteria from Soils through an Educational Project and Their Evaluation as Potential Biocontrol Agents

“…In addition, Le Han et al 2022 [32] isolated strains of B. halotolerans and B. laterosporus from marine sediment samples that produced thermostable and pH-tolerant antifungal compounds, which inhibited the growth of relevant pathogens such as Alternaria alternata, Candida albicans, Cladosporium sp., Trichophyton rubrum, Trichosporon pullulans, and F. oxysporum. The data obtained in this study corroborate the antibacterial capacity of B. laterosporus, which has also been previously detected in soil samples by our research group [27].…”

“…A total of 1220 bacteria were isolated, of which, 18 APB were identified, representing 1.5% of the total recovered isolates. These results are similar to those carried out during the former study conducted by Fernández-Fernández et al 2022 [27], in which only 1.2% of total tested isolates were selected as potential antimicrobial producers.…”

“…Subsequently, these 52 isolates were subjected to a second screening in the laboratory of the University of La Rioja. Thus, the antimicrobial activity was evaluated against 12 indicator bacteria using the Spot-on-Lawn method [27] and after rigorous repetitions, 18 out of the 52 bacteria isolated were finally selected because of their clear antimicrobial activity against at least one indicator bacteria and were considered as APB (Figure 1B and Table 1).…”

“…We have previous experience in the development of the MicroMundo project in the region of La Rioja (Spain) in 2019 [26] and 2020-2022 [27]. After the success achieved in those years in terms of citizen participation and awareness of the AMR problem, we continued the project in 2023, looking not only for antimicrobial-producing bacteria (APB), but also for those of interest as potential biocontrol agents.…”

Green Antimicrobials

“…They collected soil samples from different areas and analyzed their content for antimicrobial-producing bacteria. In total, 132 potentially producing bacteria were identified, from which 18 isolates were deemed low producers of antimicrobial agents, 12 were recognized as medium producers, and 2 were considered highly antimicrobial-producing isolates [4]. Aside from soil, agricultural wastes can also serve as sources of antimicrobial agents.…”