Objective: Objective 1. Test increasingly practical wetting agents for drag and bootie swabs.
Objective 2. Validate optimal wetting agent for the drag and bootie swabs on varying soil created by various stages of ground preparation for different commodities.
Abstract: Aggregative sampling methods, such as drag and bootie swabs, have been studied in animal and produce production but have not been fully optimized for produce – for example the typical wetting agent is evaporated milk, which is a potential allergen, animal sourced, and not shelf stable. Thus, there is a need to optimize wetting agent composition for drag and bootie swabs of produce soil. In this proposal, we use soil composite grabs as a reference to ensure the aggregation is valid and evaporated milk as a reference to ensure the optimization for wetting agents is valid. Three sample schemes will be used to collect samples, paired steps and scoops, scoping at some steps, and walking a serpentine pattern. In objective 1, we will compare evaporated milk, buffered peptone water, neutralizing buffer, and phosphate-buffered saline wetting agents for organism recovery from soil sprayed with untreated-manure, over up to 6 months of for die-off. Aerobic count recovery, total coliforms, and generic E. coli will be tested for microbial quality and safety purposes. Compared to reference methods, the drag and bootie swabs hydrated with optimal wetting agent could be (i) more practical if it was clean label, easier to use, faster to collect samples, and less labor; and (ii) more powerful if it would show at least as good, if not better, results for bacteria recovery abilities. In objective 2, drag and bootie swabs will be hydrated by the optimal wetting agent and tested on three commodities in sustainable student farms and two commodities in specialty crop farms. For each commodity, we will collect samples on tilled soil, immediately or 1-2 days post-irrigation, and after opportunity events like rainfall or animal intrusion. The bacteria recovery ability will be analyzed by plate counts and enrichment. 16s rRNA sequencing will be used to test bacteria diversity. We will keep track of the soil parameters, such as texture, pH, soil organic carbon, and microbial biomass, every visit for both objectives 1 and 2. The goal of this project is to enable evidence-based changes in produce soil sampling through industry and academia to ultimately allow producers to better protect public health by evaluating food quality and safety indicators.