Skip to main content
ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Produce Safety and Microbiology Research » Research » Publications at this Location » Publication #144900

Title: DIFFERENCES IN ATTACHMENT OF SALMONELLA ENTERICA AND ESCHERICHIA COLI O157:H7 TO ALFALFA SPROUTS

Author
item Barak Cunningham, Jeri
item Whitehand, Linda
item CHARKOWSKI, AMY

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2002
Publication Date: 10/20/2002
Citation: BARAK CUNNINGHAM, J.D., WHITEHAND, L.C., CHARKOWSKI, A. DIFFERENCES IN ATTACHMENT OF SALMONELLA ENTERICA AND ESCHERICHIA COLI O157:H7 TO ALFALFA SPROUTS. APPLIED AND ENVIRONMENTAL MICROBIOLOGY. 2002.68(10)4758-4763

Interpretive Summary: Numerous human bacterial outbreaks have been associated with contaminated sprouts. We examined how pathogenic and non-pathogenic bacteria isolated from alfalfa sprouts grow on and adhere to alfalfa sprouts. Growth on and adherence to sprouts was not significantly different among different pathogenic bacterial serovars, but all Salmonella grew on and adhered to alfalfa sprouts significantly better than E. coli O157:H7. E. coli O157:H7 was essentially rinsed from alfalfa sprouts with repeated washing steps, while 10 to 100 Salmonella remained attached per sprout. Salmonella adhered to three-day-old sprouts as well as non-pathogenic plant associated bacteria, whereas the growth rates of all four bacteria throughout seed sprouting were similar. Salmonella and plant-associated bacteria adhered 10 to 1000-fold greater than E. coli O157:H7; however three of four other E. coli serotypes, isolated from cabbage roots exposed to sewage water following a spill, adhered to sprouts better than E. coli O157:H7 and as well as the non-pathogenic plant assoicated bacteria strains. Therefore, attachment to alfalfa sprouts among E. coli serotypes is variable and non-pathogenic strains of E. coli to be used as surrogates for the study of pathogenic E. coli may be difficult to identify and should be selected carefully with knowledge of the biology being examined.

Technical Abstract: Numerous Salmonella enterica and Escherichia coli O157:H7 outbreaks have been associated with contaminated sprouts. We examined how S. enterica serovars, E. coli serotypes, and non-pathogenic bacteria isolated from alfalfa sprouts grow on and adhere to alfalfa sprouts. Growth on and adherence to sprouts was not significantly different among different serovars of S. enterica, but all S. enterica serovars grew on and adhered to alfalfa sprouts significantly better than E. coli O157:H7. E. coli O157:H7 was essentially rinsed from alfalfa sprouts with repeated washing steps, while 1 to 2 log S. enterica remained attached per sprout. S. enterica Newport adhered to three-day-old sprouts as well as Pantoea agglomerans, and 10-fold greater than Pseudomonas putida and Rahnella aquatilis , whereas the growth rates of all four strains throughout seed sprouting were similar. S. enterica Newport and plant-associated bacteria adhered 10 to 1000-fold greater than E. coli O157:H7; however three of four other E. coli serotypes, isolated from cabbage roots exposed to sewage water following a spill, adhered to sprouts better than E. coli O157:H7 and as well as the Pseudomonas and Rahnella strains. Therefore, attachment to alfalfa sprouts among E. coli serotypes is variable and non-pathogenic strains of E. coli to be used as surrogates for the study of pathogenic E. coli may be difficult to identify and should be selected carefully with knowledge of the biology being examined.