Growth of Salmonella During Sprouting of Alfalfa Seeds Associated with Salmonellosis Outbreaks

D.S. Stewart, K.F. Reineke, J.M. Ulaszek, and M.L. Tortorello

Journal of Food Protection, Vol. 64, No 5, 2001, Pages 618-622

Abstract
Growth of Salmonella was assessed during sprouting of naturally contaminated alfalfa seeds associate with two outbreaks of salmonellosis.  Salmonella was determined daily in sprouts and sprout rinse water samples by a three-tube most probable number (MAN) procedure and a commercial enzyme immunoassay (EIA).  Growth of Salmonella in the sprouts was reflected in the rinse water, and the MPNs of the two samples were generally in agreement within approximately 1 log.  The results from EIA testing of sprouts and water samples were also in agreement.  The pathogen was present in the seed at less than 1 MAN/g, and it increased in number to maximum population levels of 10² to 10³ MAN/g in one seed lot and 10² to 10⁴ MAN/g in the other seed lot.  Maximum populations of the pathogen were apparent by day 2 of sprouting.  These results show the ability of the pathogens to grow to detectable levels during the sprouting process, and they provide support for the recommendations to test the sprout water for the presence of pathogens 48 h after starting seed sprouting.  The effectiveness of a 10-min, 20,000-ug/ml (ppm) calcium hypochlorite treatment of the outbreak-associated seeds was studied.  For both seed lots, the hypochlorite treatment caused a reduction, but not elimination, of Salmonella contamination in the finished sprouts.  These results confirm the need to test each production batch for the presence of pathogens, even after 20,000 ug/ml (ppm) hypochlorite treatment of seeds, so that contaminated product is not distributed.