Evaluation of the occurrence of sporulating and nonsporulating pathogenic bacteria in manure and in digestate of five agricultural biogas plants

The number of agricultural biogas plants has been increasing in the past decades in some European countries. Digestates obtained after anaerobic digestion (AD) of manure are usually spread on agricultural land; however, their hygiene status regarding pathogens posing public health and/or animal health challenges has been poorly characterized up to now in France. In this study, three replicates of manure and digestate were collected from five farm biogas plants receiving animal manure in order to assess the occurrence and concentrations of sporulating (Clostridium botulinum, Clostridioides difficile, Clostridium perfringens) and nonsporulating (Listeria monocytogenes, thermotolerant Campylobacter spp., Salmonella, Escherichia coli, enterococci) bacteria. Concentrations of E. coli, enterococci, and C. perfringens in digestates ranged from 102 to 104, 104 to 105, and