A Framework for Developing Research Protocols for Evaluation of Microbial Hazards and Controls during Production That Pertain to the Application of Untreated Soil Amendments of Animal Origin on Land Used To Grow Produce That May Be Consumed Raw

Abstract

Application of manure or soil amendments of animal origin (untreated soil amendments; UTSAs) to agricultural land has been a long-standing practice to maintain or improve soil quality through addition of organic matter, nitrogen, and phosphorus. Much smaller quantities of these types of UTSAs are applied to land used for food crops than to land used for animal grain and forage. UTSAs can harbor zoonotic enteric pathogens that may survive for extended periods after application. Additional studies are needed to enhance our understanding of preharvest microbial food safety hazards and control measures pertaining to the application of UTSAs especially for land used to grow produce that may be consumed raw. This document is intended to provide an approach to study design and a framework for defining the scope and type of data required. This document also provides a tool for evaluating the strength of existing data and thus can aid the produce industry and regulatory authorities in identifying additional research needs. Ultimately, this framework provides a means by which researchers can increase consistency among and between studies and facilitates direct comparison of hazards and efficacy of controls applied to different regions, conditions, and practices.

Development of an Avirulent Salmonella Surrogate for Modeling Pathogen Behavior in Pre- and Postharvest Environments

“…However, field experiments with virulent human pathogens are unlikely to receive regulatory approval due to the obvious risks associated with environmental exposure. Surrogate organisms have been used to better understand how human pathogens survive in environments and respond to mitigation treatments (15)(16)(17). Surrogates are deliberately introduced in order to assess the effectiveness of disinfection, sanitation, or other treatments (17).…”

“…Avirulent strains of human pathogens or closely related nonpathogenic species are the most commonly used surrogates (15,16). For example, naturally occurring mutants of E. coli O157:H7 lacking stx genes (encoding Shiga toxins) and containing a plasmid-borne green fluorescent protein have been used in field experiments to assess the effects of irrigation types and exposure to sunlight on the ability of the pathogen to colonize specific sites on plants and to persist on crops (18)(19)(20).…”

“…Recent framework documents took into consideration an expanded molecular biology toolset and provided additional clarification on the issue (15, 16). For example, it is suggested that the surrogate not only should be avirulent (for example, due to a regulatory mutation) but should lack virulence genes altogether (15,16).Avirulent strains of human pathogens or closely related nonpathogenic species are the most commonly used surrogates (15,16). For example, naturally occurring mutants of E. coli O157:H7 lacking stx genes (encoding Shiga toxins) and containing a plasmid-borne green fluorescent protein have been used in field experiments to assess the effects of irrigation types and exposure to sunlight on the ability of the pathogen to colonize specific sites on plants and to persist on crops (18)(19)(20).…”

“…Surrogates should be easily culturable and distinguishable from the background microbiota (17). Recent framework documents took into consideration an expanded molecular biology toolset and provided additional clarification on the issue (15,16). For example, it is suggested that the surrogate not only should be avirulent (for example, due to a regulatory mutation) but should lack virulence genes altogether (15,16).…”

Effects of nitrogen and potassium fertilization on the susceptibility of tomatoes to post-harvest proliferation of Salmonella enterica

“…For the inocula, the type strain S. enterica sv Typhimurium ATCC14028 or strains of S. enterica (Javiana ATCC BAA-1593, S. Montevideo LJH519, S. Newport C6.3, S. Braenderup 04E01347, 04E00783, 04E01556) linked to the human outbreaks of salmonellosis were individually grown overnight at 37 C in LB broth with shaking. They were then washed twice in phosphate-buffered saline (pH 7.0), and the strains from the outbreaks were combined into a six-strain "cocktail" as suggested by the Framework for Evaluation of Microbial Hazards (Harris et al, 2012;Harris et al, 2013). These inocula were further diluted in sterile water and 3 ml of the suspension (containing between 100 and 1000 CFU) were spotted onto three shallow (w1 mm) wounds in tomato epidermis.…”