Plant-Scale Validation of Physical Heat Treatment of Poultry Litter Composts Using Surrogate and Indicator Microorganisms for Salmonella

This study selected and used indicator and surrogate microorganisms for Salmonella to validate the processes for physically heat-treated poultry litter compost in litter processing plants. Initially laboratory validation studies indicated that 1.2- to 2.7-log or more reductions of desiccation-adapted Enterococcus faecium NRRL B-2354 were equivalent to > 5-log reductions of desiccation-adapted Salmonella Senftenberg 775/W in poultry litter compost, depending on treatment conditions and compost types. Plant validation studies were performed in one turkey litter compost processor and one laying hen litter compost processor. E. faecium was inoculated at ca.7 log CFU g^-1 into the turkey litter compost and at ca. 5 log CFU g^-1 into laying hen litter compost with respectively targeted moisture contents. The thermal processes in the two plants yielded 2.8 - > 6.4 log CFU g^-1 (> 99.86%) reductions E. faecium of the inoculated. Similarly, for the processing control samples, reductions of presumptive indigenous enterococci were in the order of 1.8-3.7 log CFU g^-1 (98.22% to 99.98%) of the total naturally present. In contrast, there were less reductions of indigenous mesophiles (1.7-2.9 log CFU) and thermophiles (0.4-3.2 log CFU g^-1). More indigenous enterococci were inactivated in the presence of higher moisture in the poultry litter compost. Based on the data collected under the laboratory conditions, the processing conditions in both plants were adequate to reduce any potential Salmonella contamination of processed poultry litter compost by at least 5 logs, even though the processing conditions varied among trials and plants.IMPORTANCE Poultry litter compost, commonly used as a biological soil amendment, is subjected to a physical heat-treatment in industry setting to reduce pathogenic bacteria such as Salmonella and produce a dry product. According to the FDA Food Safety Modernization Act (FSMA) Produce Safety Rule, the thermal process for poultry litter compost should be scientifically validated to satisfy the microbial standard requirement. To the best of our knowledge, this is the first validation study in commercial poultry litter compost processing plants, and our results indicated that Salmonella levels, if present, could be reduced by at least 5 logs based on the reductions of surrogate and indicator microorganisms, even though the processing conditions in these commercial plants varied greatly. Furthermore, both indicator and surrogate microorganisms along with the custom-designed sampler can serve as practical tools for poultry litter compost processors to routinely monitor or validate their thermal processes without introducing pathogens into the industrial environments.

Bacterial Community Dynamics Distinguish Poultry Compost from Dairy Compost and Non-Amended Soils Planted with Spinach

The aim of this study was to determine whether and how poultry litter compost and dairy manure compost alter the microbial communities within field soils planted with spinach. In three successive years, separate experimental plots on two fields received randomly assigned compost treatments varying in animal origin: dairy manure (DMC), poultry litter (PLC), or neither (NoC). The composition and function of bacterial and fungal communities were characterized by the amplicon sequencing of marker genes and by the ecoenzyme activity, respectively. The temporal autocorrelation within and among years was adjusted by principal response curves (PRC) to analyze the effect of compost on community composition among treatments. Bacteria in the phylum Bacteriodetes, classes Flavobacteriia and Spingobacteriales (Fluviicola, Flavobacteriia, and Pedobacter), were two to four times more abundant in soils amended with PLC than DMC or NoC consistently among fields and years. Fungi in the phylum Ascomycota were relatively abundant, but their composition was field-specific and without treatment differences. The ecoenzyme data verify that the effects of PLC and DMC on soil communities are based on their microbial composition and not a response to the C source or nutrient content of the compost.