Purpose: This study was to investigate the survival of Escherichia coli O157:H7 and Salmonella Typhimurium in compost with different particle sizes as affected by initial moisture content and seasonality under greenhouse condition.
Methods: The mixture of avirulent S. Typhimurium and E. coli O157:H7 were inoculated into the finished compost with initial moisture content of 20%, 30% and 40%. Then, the finished compost samples were sieved into three portions with particle size of >1000, 500-1000 and <500 μm, and stored in greenhouse for 30 days. At selected intervals, compost samples were tested for pathogen population.
Results: The moisture contents in compost samples dropped to under 10% within 5 days of storage followed by gradual decline till 30 days in all treatments. For moisture contents of 20 and 30%, the average Salmonella reductions in compost with particle sizes of >1000, 500-1000 and <500 μm were 2.15, 2.27 and 2.47 log CFU/g within 5 days of storage in summer, respectively, as compared with 1.60, 2.03 and 2.26 log CFU/g in late fall, and 2.61, 3.33 and 3.67 log CFU/g for winter, respectively. E. coli O157: H7 reduction in compost with particle sizes followed the same trend as Salmonella.
Significance: Our results revealed that compost with larger particle size supports pathogen survival more than the compost with small particle size, and the initial rapid moisture loss in compost contributes to fast inactivation of pathogens in the finished compost.