Survival of Escherichia coli O157:H7 and Salmonella enterica in animal waste-based composts as influenced by compost type, storage condition and inoculum level.

AIM: Survival of Escherichia coli O157:H7 and Salmonella enterica in animal waste-based composts was studied with different compost types, storage conditions and inoculum levels.

METHODS AND RESULTS: A cocktail of three E. coli O157:H7 or S. enterica strains was inoculated into dairy manure-based composts (A and B) or poultry litter-based composts (C and D), respectively, at final concentrations of c. 5 or 2 log CFU per gram. Composts were then stored at 5 and 22°C, and under greenhouse condition. Both pathogens survived better at 5 than 22°C and under greenhouse conditions. Escherichia coli O157:H7 at both inoculation levels survived for >168 days in composts A and B under at 5°C, whereas the longest survival of S. enterica at both inoculation levels was observed to be >168 days in compost C at 5°C. Overall, composts A and C provided better survival conditions for E. coli O157:H7 and S. enterica, respectively, and both pathogens at the high inoculum level survived better as compared to the low inoculum level.

CONCLUSIONS: Escherichia coli O157:H7 and S. enterica could potentially survive for long periods of time in dairy and poultry composts. Some factors influencing the pathogen survival included compost type, storage condition and inoculum level.

SIGNIFICANCE AND IMPACT OF THE STUDY: Our results have provided scientific data on the pathogen survival in dairy and poultry composts, which could be used for the risk assessment of using animal waste-based composts as biological soil amendments.