Purpose: To evaluate the influence of soil type, nutrient availability and microbial community composition (MCC) on the survival of EcO157 in the spinach rhizosphere.
Methods: Four soil types were inoculated with a mixture of two stx-minus EcO157 under growth chamber, greenhouse and field conditions. Organic crops were fertilized by application of chicken pellets (8:1:1) at 90, 180 and 270 kg/ha to soil. Conventional soils received total nitrogen applications of 112, 224, and 336 kg/ha. Growth chamber inoculum was log 2.1 CFU/g soil and incubation temperatures of 15 and 25 °C. Greenhouse inoculum was log 2.3 CFU/g soil. Field inoculum was log 4.6 CFU/g sachet. Inoculations were done after sowing or at two true-leaves. Soil physicochemical analysis included total carbon, nitrogen, pH and electrical conductivity. Total MCC and diversity was estimated by using phospholipid fatty acid analysis (PLFA).
Results: Growth chamber-Greenhouse A significant positive correlation between the survival of EcO157, soil clay content, and chicken pellet rate was observed (P < 0.05). Time to non-detection of EcO157 was shorter in conventional than organic sandy loam soils (30 vs. 45 days, respectively). In conventional soils, nitrogen availability <224 kg/ha and 15 °C extended the survival of EcO157 (P < 0.05). Conventional fields. No correlation was observed between N availability and pathogen survival; however, greater survival was observed in Sandy Loam than Loamy Sand soils (60 vs. 31 days, respectively (P < 0.05)). Overall, PLFA analysis indicated that greater microbial community diversity and biomass was associated with faster die-off of EcO157, irrespective of soil type and farming practice.
Significance: Development of RFP intended to limit human pathogen persistence in cultivated soils should consider the soil physicochemical characteristics as a focal point for preventive controls or mitigations.