Contamination of spinach at germination: A route to persistence and environmental reintroduction by Salmonella

Authors: KUMAR, GOVINDRAJ - University Of Georgia; Patel, Jitu; RAVISHANKAR, SADHANA - University Of Arizona

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2020
Publication Date: 5/12/2020
Citation: Kumar, G., Patel, J.R., Ravishankar, S. 2020. Contamination of spinach at germination: A route to persistence and environmental reintroduction by Salmonella. International Journal of Food Microbiology. https://doi.org/10.1016/j.ijfoodmicro.2020.108646.
DOI: https://doi.org/10.1016/j.ijfoodmicro.2020.108646

Interpretive Summary: Foodborne illnesses associated with consumption of fresh produce have increased in recent years. Pathogen contamination of fresh produce via irrigation water at the farm level has been well documented. Persistence of contaminated pathogen on fresh produce leaf varied with left morphology of cultivars. We evaluated the effect of contaminated seeds and water on the persistence and internalization of Salmonella Newport in different cultivars of spinach. Salmonella populations were recovered from spinach seeds which were contaminated either by immersion in Salmonella suspension prior to germination or germinated in contaminated water. Further, Salmonella internalized into leaves and steam of the spinach plants via root uptake. The Salmonella internalization into spinach leaves varied with the routes of seed contamination. Salmonella were also recovered from soil and water runoff samples. The spinach growers can use these results to minimize seed contamination with pathogens and subsequent foodborne illnesses.

Technical Abstract: The effects of using contaminated seed & water, on the persistence and internalization of Salmonella Newport in organic spinach cultivars- Lazio, Space, Emilia & Waitiki were studied. Seeds were contaminated by either immersing in a suspension of Salmonella and then germinated or were germinated in Salmonella contaminated water in the dark at 25oC. After 5 days, germinated sprouts were analyzed for S. Newport population & internalization. Germinated seedlings were potted in soil and grown in a plant incubator for 4 weeks. Leaves, stems & roots were sampled for Salmonella population by plating on CHROMagar. Plants Surface-sterilized with chlorine were analyzed for internalized pathogen. Potting soil & water runoff were sampled for Salmonella after 4 weeks of plant growth. Contaminated seeds & irrigation water had S. Newport populations of 7.64±0.43 log CFU/g and 7.12±0.04 log CFU/ml, respectively. Seedlings germinated using contaminated water & seeds had S. Newport populations of 8.09±0.04 and 8.08±0.03 log CFU/g, respectively. Populations of S. Newport in leaves, stem & roots of spinach plants were as follows: contaminated seed- 2.82±1.69, 1.69±0.86, and 4.41±0.62 log CFU/ml; contaminated water- 3.56±0.90, 3.04±0.31, and 4.03±0.42 log CFU/ml of macerated tissue suspension, respectively. Internalization was observed in plants developing from contaminated seed & in sprouts germinated using contaminated water. S. Newport populations of 2.82±0.70 log CFU/g and 1.76±0.46 log CFU/ml were recovered from soil & water runoff, respectively. The results indicate that contamination of spinach during germination can result in persistence, internalization and environmental reintroduction of Salmonella.