Background:
Microbial food safety risks remain a significant global concern. Horticulture products consumed raw represent a high-risk food category. Pathogens from the environment may contaminate fresh produce, survive human digestion, enter the gut and cause disease. Foodborne pathogen transmission throughout horticultural supply chains has been well-characterised. However, the transfer of entire environmental microbiomes onto fresh produce, and subsequently into the gut, remains unclear. Of all horticultural production inputs, water has one of the largest impacts on fresh produce quality and safety. The aim of this study was thus to investigate: (1) how irrigation water microbiomes influence the fresh produce microbiome; (2) how these microbiomes survive subsequent human digestion; and (3) their relationships to foodborne pathogen transmission.
Methods:
Cut spinach was employed as a model system due to its ready-to-eat nature and food safety relevance. Briefly, multiple irrigation events were simulated by soaking spinach in drain water (fresh and autoclave-sterilised). Some events involved spiking drain water with challenge concentrations of two foodborne pathogens, Escherichia coli O157 and Salmonella Typhimurium. In these cases, portions of soaked spinach underwent simulated human digestion using the in vitro Infogest model. Remaining spinach was incubated aerobically and subsampled at multiple timepoints thereafter for culture-based microbial quantitation and 16S microbiome profiling.
Results:
Results indicated that water microbiomes could transiently impact fresh produce microbiomes via one-off contact events. During a 10-day refrigeration period, no significant reduction (p > 0.05) in inoculated pathogens was observed despite substantial temporal changes in the spinach microbiome. Furthermore, most of the E. coli, Salmonella and total microbial loads in soaked spinach survived simulated digestion, denoting consistent, effective transmission to the gut.
Conclusions:
This research offers preliminary insight into the role of fresh produce irrigation water in mediating environment-to-human microbiome transmission. Elucidating these microbiome-pathogen dynamics further may reveal novel targets for enhancing food safety.