Cross-Kingdom Antagonistic Interactions Between Environmental Antibiotic-Resistant Bacteria and Yeasts in Pastoral Ecosystems

Pasture-based farming systems remain understudied as a source of antibiotic-resistant bacteria and antagonistic yeasts under low-input management. In this study, soil, feed, and freshwater samples from Lithuanian farms were analyzed to characterize resistance phenotypes and inhibitory interactions among cultivable microorganisms. Bacterial and yeast isolates, representing 14 and 9 genera, respectively, were identified using molecular methods. Bacterial isolates recovered under antibiotic-selective conditions exhibited resistance to at least one of four antibiotics (ampicillin, streptomycin, tetracycline, chloramphenicol), with 41% showing multidrug resistance and the highest frequencies observed for ampicillin (59%) and streptomycin (48%). Microbial distribution was habitat-specific, with soil containing the highest diversity of antibiotic-resistant bacteria and feed samples harboring the greatest abundance of yeasts. Functional assays demonstrated consistent antagonistic activity of several Wickerhamomyces anomalus strains against susceptible yeasts and antibiotic-resistant Bacillus spp. These findings highlight the coexistence of resistance and antagonistic traits in pasture-associated microbiota and suggest their potential interaction under controlled conditions.