Native Bacterial Communities and Listeria Monocytogenes Survival in Soils Collected from the Lower Mainland of British Columbia, Canada

Soil is an important reservoir for Listeria monocytogenes, a foodborne pathogen implicated in numerous produce-related outbreaks. Our objectives were to (i) compare the survival of L. monocytogenes among three soils, (ii) compare the native bacterial communities across these soils, and (iii) investigate relationships between L. monocytogenes survival, native bacterial communities, and soil properties. Listeria spp. populations were monitored on PALCAM agar in three soils inoculated with L. monocytogenes (∼5 × 106 CFU/g): conventionally farmed (CS), grassland transitioning to conventionally farmed (TS), and uncultivated grassland (GS). Bacterial diversity of the soils was analyzed using 16S rRNA targeted amplicon sequencing. A 2 log reduction of Listeria spp. was observed in all soils within 10 days, but at a significantly lower rate in GS (Fisher's least significant difference test; p < 0.05). Survival correlated with increased moisture and a neutral pH. GS showed the highest microbial diversity. Acidobacteria was the dominant phylum differentiating CS and TS from GS, and was negatively correlated with pH, carbon, nitrogen, and moisture. High moisture content and neutral pH are likely to increase the ability of L. monocytogenes to persist in soil. This study confirmed that native bacterial communities and short-term survival of L. monocytogenes varies across soils.