Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2004
Publication Date: 4/1/2004
Citation: Islam, M., Morgan, J., Doyle, M.P., Phatak, S.C., Millner, P.D., Jiang, X. 2004. Fate of Salmonella enterica serovar Typhimurium on carrots and radishes grown in fields treated with contaminated manure composts or irrigation water. Foodborne Pathogens and Disease. 70:2497-2502. Interpretive Summary: Foodborne illness outbreaks have raised interest in identifying pre- and postharvest sources that can contaminate raw and minimally processed fruits and vegetables. Raw or improperly composted (still contaminated) manure, contaminated irrigation water, runoff from pastureland, or excreta from wild animals that transit through crop areas and bring pathogens into direct contact with produce. Enteric pathogens (e.g., E. coli O157:H7 and Salmonella) that have the potential for growth prior to consumption or have a low infectious dose are of special concern as contaminants of fruits and vegetables. In this field study we examined the persistence and fate of an avirulent strain of S. enterica serovar Typhimurium on carrots and radishes and in surrounding soil when manure composts of different types or irrigation water contaminated with salmonellae are applied to soil in fields typical of those used for vegetable production. In this study, three properly composted manures (poultry, dairy, straw-old silage-bedding) were seeded with the S. Typhimurium at a rate of 10 billion cells per gram; compost was applied at 4.5 mt/ha in rows. Contaminated irrigation water was inoculated with 105 S. Typhimurium /ml and was sprayed with a hand sprayer on each of the 5 plots for each crop only once. Results indicate that pathogen-containing irrigation water or composted manure can play an important role in contaminating carrots and radishes and the soil in which they grow. Results show the importance of using disinfected irrigation water, and hence proper maintenance of irrigation wells need to be maintained properly. All irrigation water should be monitored for human pathogenic microorganisms or suitable indicators of pathogen contamination. Manure used as fertilizer or as a soil amendment should be treated to eliminate pathogenic microorganisms (e.g., proper time-temperature criteria used for composting). A minimum amount of time (e.g., at least 240 days) also should be scheduled between the final application of manure to fields and harvest. These studies have identified important factors that can contribute to Salmonella contamination of produce, which should be addressed by produce growers in managing their fields This information will help inform growers, produce packers, scientists, and others interested in preventing pre-harvest produce contamination. These studies have identified important factors that can contribute to Salmonella contamination of produce, which should be addressed by produce growers in managing their fields.
Technical Abstract: Three different types of composts, PM-5 (poultry manure compost), 338 (dairy manure compost) and NVIRO-4 (alkaline stabilized dairy manure compost), and irrigation water were inoculated with an avirulent strain of Salmonella enterica serovar Typhimurium at 107 cfu g-1 and 105 cfu ml-1, respectively, to determine the persistence of salmonellae in soils containing these composts or irrigation water, and also on two root vegetables, carrots and onions, grown in these contaminated soils. Compost was applied to soil as a strip at a rate of 4.5 metric tons/hectare before carrots and radishes were seeded. A split-plot block design plan was used for each crop, with five treatments (one without compost, three with each of the three composts, and one without compost but with contaminated water applied) and five replicates for a total of 25 plots for each crop. Each plot measured 1.8 x 4.6 meters. Salmonella persisted for an extended period of time, with the bacteria surviving in soil samples for 203 to 231 days, and detected for 84 and 203 days on radishes and carrots, respectively. Survival profiles of Salmonella on vegetables and soil samples contaminated by irrigation water were similar to those observed when contamination occurred through compost. Hence, both contaminated manure compost and irrigation water can play an important role in contaminating soil and root vegetables with Salmonella for several months.