Physicochemical and microbial properties of dairy barn soils: a case study in Costa Rican farm-associated soils harboring the foodborne pathogen Listeria monocytogenes

Abstract

Animal farming activities can influence soil properties that contribute to the survival of foodborne pathogens like the ubiquitous Listeria monocytogenes. However, the presence of this pathogen in farm-associated soils in Costa Rica has not been studied, which might provide new insights regarding the environmental conditions associated with the establishment of this pathogen. In this work, we correlated the presence of L. monocytogenes with the soil physicochemical properties and bacterial community structure of soils associated with livestock activities, including a dairy barn floor (DB) and a slaughterhouse holding pen (SH). A cropland (CL) was included as an example of soil not associated with animal farming practices. We characterized the presence pattern of L. monocytogenes via culture-dependent and culture-independent techniques (i.e., metabarcoding based on 16S rRNA gene sequencing) and conducted a determination of physical, elemental and chemical parameters with Fourier-transform infrared spectroscopy (FT-IR) to statistically determine the soil properties that correlate with L. monocytogenes’ presence in the soil. L. monocytogenes was isolated from DB samples and SH but not from CL. Subsequently, 16S rRNA gene-based metabarcoding showed that the presence of L. monocytogenes was positively correlated with higher bacterial diversity, while physicochemical analyses revealed that the total hydrogen and nitrogen contents of soil organic matter, pH, and electrical conductivity were the main drivers of L. monocytogenes’ presence. Moreover, a CL sample fertilized with animal-derived products showed DB-like physicochemical properties matching conditions in favor of L. monocytogenes’ presence. Hence, our work emphasizes the significance of soil as a primary source for the widespread dissemination of pathogens, particularly underscoring the necessity for improved agricultural practices to prevent cross-contamination with L. monocytogenes. Additionally, we highlight the importance of further understanding the biotic and abiotic factors in facilitating the establishment of L. monocytogenes.