Selection of Indigenous Indicator Microorganisms for Validating Desiccation-adapted Salmonella Reduction in Physically Heat-treated Poultry Litter

Introduction: Physical heat treatment is commonly used to eliminate human pathogens, such as Salmonella, in poultry litter as organic fertilizer. However, it is not feasible in poultry litter processing facility to validate thermal processes with pathogenic bacteria.

Purpose: The objective of this study was to compare the thermal inactivation of desiccation-adapted Salmonella with that of indigenous indicator microorganisms in poultry litter.

Methods: Aged broiler litter and composted turkey litter with 20, 30, 40, and 50% moisture contents were inoculated with desiccation-adapted Salmonella Senftenberg (ca. 10⁷ log CFU/g) and then heat-treated at 75 and 85°C for 3 h. The surviving populations of Salmonella Senftenberg, indigenous enterococci, and total aerobic bacteria were enumerated. 

Results: Compared to total aerobic bacteria, there were better correlations between mean log reductions of desiccation-adapted Salmonella Senftenberg and indigenous enterococci in broiler litter samples with 20, 30, 40, and 50% moisture contents at 75^oC (R²>0.91), and 20, 30, and 40% moisture contents at 85°C (R²>0.87). Mean log reductions of S. Senftenberg were better correlated with those of indigenous enterococci in turkey litter samples with 20, 30, 40, and 50% moisture contents at 75°C (R²>0.88), and 20 and 30% moisture contents at 85°C (R²=0.83) than those of total aerobic bacteria, which had a better correlation in turkey litter sample with 40% (R²=0.98) moisture content at 85°C.

Significance: Our results demonstrated that indigenous enterococci may be used to validate the thermal processing of poultry litter as it mimics the survival behavior of Salmonella during heat treatment.