Differences in Attachment of Salmonella Enterica Serovars and Escherichia Coli O157 H7 to Alfalfa Sprouts

Differences in Attachment of Salmonella enterica Serovars and Escherichia coli O157:H7 to Alfalfa Sprouts

Applied and Environmental Microbiology, October 2002, p. 4758-4763, Vol. 68, No. 10
American Society for Microbiology.

J. D. Barak,* L. C. Whitehand, and A. O. Charkowski

Produce Safety and Microbiological Research, Western Regional Research Center, USDA Agricultural Research Service, Albany, California 94710

Received 15 April 2002/ Accepted 4 July 2002

Numerous Salmonella enterica and Escherichia coli O157:H7 outbreaks have been associated with contaminatedsprouts. We examined how S. enterica serovars, E. coli serotypes, and nonpathogenic bacteria isolated from alfalfa sprouts grow on and adhere to alfalfa sprouts. Growth on and adherence to sprouts were 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 alfalfasprouts with repeated washingsteps, while 1 to 2 log CFU of S. enterica remained attachedper sprout. S. enterica Newport adhered to 3-day-oldsprouts as well as Pantoea agglomerans and 10-fold more 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 1,000-fold more than E. coli O157:H7; however, three of four other E. coliserotypes, 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 alfalfasprouts among E. coli serotypes is variable, and nonpathogenic 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.

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