Earthworm Casts as Selective Microhabitats Enriching Antagonistic Bacteria with in Vitro Inhibitory Potential against Enteric Bacterial Pathogens
DOI:
https://doi.org/10.33003/fjs-2026-1010-5423Keywords:
Antibacterial, Antibiosis, Biocontrol, VermicompostAbstract
Earthworm casts as biologically active microhabitats significantly influence soil microbial compositions and activities. Analysis was conducted to evaluate the diversity and antagonistic potential of bacterial isolates in the casts of earthworm and adjacent soil against some selected enteric bacterial pathogens. A total of 30 bacterial isolates, comprising 18 isolates from earthworm casts and 12 isolates from the soil samples, were obtained. Morphological and biochemical characterization revealed the presence of dominant genera, including: Bacillus spp., Streptomyces spp., and Pseudomonas spp. Antagonistic activity was assayed using the agar well diffusion method against Escherichia coli, Salmonella spp., and Klebsiella spp. Among the total isolates obtained, 14 (46.7%) exhibited antagonistic activity, with a higher proportion originating from earthworm casts, and 10 isolates with 71.4% compared to soil, which had 4 isolates; 28.6%. The zones of inhibition ranged from 8 mm to 22 mm across all test organisms. Bacillus spp. demonstrated the highest inhibitory activity with a mean zone of 18 mm, followed by Streptomyces spp. (15 mm), while Pseudomonas spp. showed a comparatively lower activity. Escherichia coli was the most susceptible test pathogen, exhibiting a maximum inhibition zone of 22 mm, whereas Klebsiella spp. showed the least susceptibility with a minimum inhibition reading of 10 mm. Negative control experiments showed no zones of inhibition, confirming that antimicrobial effects were exclusively due to metabolites produced by the assayed bacterial isolates. The outcome of the finding suggests that earthworm cast may serve as a selective microenvironment that enriches bacterial populations with significant antagonistic potentials.
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Copyright (c) 2026 Collins Chukwunalu Ossai, Edward Ikenna Odum, Loveth Ngozi Bernard
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