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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Produce Safety and Microbiology Research » Research » Publications at this Location » Publication #136762

Title: DIFFERENCES IN GROWTH OF SALMONELLA ENTERICA AND ESCHERICHIA COLI OF O157:H7 ON ALFALFA SPROUTS

Author
item CHARKOWSKI, AMY
item Barak Cunningham, Jeri
item SARREAL, CHESTER
item Mandrell, Robert

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2002
Publication Date: 6/2/2002
Citation: Charkowski, A., Barak Cunningham, J.D., Sarreal, C.Z., Mandrell, R.E. 2002. Differences in growth of salmonella enterica and escherichia coli of o157:h7 on alfalfa sprouts. Applied and Environmental Microbiology. 68(6):3114-3120.

Interpretive Summary: Sprout producers have recently been faced with several bacterial human pathogen outbreaks. Many of the outbreaks have been traced to sprout seeds contaminated with low levels of human pathogens. Alfalfa seeds were inoculated with bacterial human pathogens isolated from alfalfa seeds or other environemtnal sources and sprouted to examine growth of these bacteria in association with sprouting seeds. Salmonella grew significatly more on sprouting seeds over 2 days,than E. coli O157:H7. The initial bacterial inoculum dose and seed-sprouting temperature significatly affected the levels of both bacteria on the sprouts and in the irrigation water, while the frequency of irrigation water replacement affected only the levels of E. coli O157:H7. Salmonella colonized both seed coats and sprout roots as aggregates, while E. coli O157:H7 colonized only sprout roots.

Technical Abstract: Sprout producers have recently been faced with several Salmonella enterica and Escherichia coli O157:H7 outbreaks. Many of the outbreaks have been traced to sprout seeds contaminated with low levels of human pathogens. Alfalfa seeds were inoculated with S. enterica and E. coli O157:H7 strains isolated from alfalfa seeds or other environemtnal sources and sprouted to examine growth of these human pathogens in association with sprouting seeds. S. enterica strains grew an average of 3.7 log10 on sprouting seeds over 2 days, while E. coli O157:H7 strains grew significatly less, an average of 2.3 log10. The initial S. enterica or E. coli O157:H7 inoculum dose and seed-sprouting temperature significatly affected the levels of both S. enterica and E. coli O157:H7 on the sprouts and in the irrigation water, while the frequency of irrigation water replacement affected only the levels of E. coli O157:H7. Colonization of sprouting alfalfa seeds by S. enterica serovar Newport and E. coli O157:H7 strains transformed with a plasmid encoding the green fluorescent protein was examined with fluorescence microscopy. Salmonella serovar Newport colonized both seed coats and sprout roots as aggregates, while E. coli O157:H7 colonized only sprout roots.