Ecological Stress Tolerance and Biofilm-Associated Persistence in Opportunistic Bacteria Isolated from Livestock Faeces

Livestock faeces constitute an important environmental interface within the One Health framework, as bacteria shed by animals are directly exposed to external environmental conditions, where they may persist and subsequently disseminate across the human, animal, and environmental sectors. The ability of these microorganisms to tolerate environmental stresses is therefore critical for their persistence and ecological distribution. In this study, the responses of 5 Pseudomonas putida, 15 Pseudomonas fulva, and 12 Alcaligenes faecalis isolates recovered from livestock faeces to different environmental stress conditions were investigated. Bacterial growth was evaluated under different temperatures, increasing NaCl concentrations, and carbon starvation, while biofilm formation was assessed using the microtiter plate assay. Growth was markedly affected by all stress conditions, although substantial variability was observed among isolates of the same species. Despite reduced growth under the most adverse conditions, all three species remained capable of growing across a wide range of environmental stresses. A. faecalis exhibited greater salt tolerance and biofilm-forming capacity than Pseudomonas spp., with biofilm formation detected in almost all isolates of both species. Furthermore, no statistically significant correlations were detected among the evaluated stress tolerance traits. These findings demonstrate that livestock-associated P. putida, P. fulva, and A. faecalis possess physiological characteristics that promote persistence under diverse environmental conditions, highlighting the potential role of livestock faeces as environmental reservoirs of opportunistic bacteria within the One Health context.