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

Abstract

Growth of Salmonella was assessed during sprouting of naturally contaminated alfalfa seeds associated with two outbreaks of salmonellosis. Salmonella was determined daily in sprouts and sprout rinse water samples by a three-tube most probable number (MPN) 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 MPN/g, and it increased in number to maximum population levels of 102 to 10(3) MPN/g in one seed lot and 10(2) to 10(4) MPN/ 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 pathogen to grow to detectable levels during the sprouting process, and they provide support for the recommendation to test the sprout water for the presence of pathogens 48 h after starting seed sprouting. The effectiveness of a 10-min, 20,0000-microg/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 microg/ml (ppm) hypochlorite treatment of seeds, so that contaminated product is not distributed.

Multistate Outbreak of Salmonella Serovar Muenchen Infections Associated with Alfalfa Sprouts Grown from Seeds Pretreated with Calcium Hypochlorite

“…While several chemical treatments can reduce Salmonella populations up to 3.2 log 10 CFU/g on alfalfa seeds, as analyzed by direct plating, no chemical treatment will eliminate the pathogen, as evidenced by detection in enrichment samples (21). Treatment of seeds with a concentration of calcium hypochlorite as high as 2% does not prevent outgrowth of Salmonella from naturally contaminated seeds (18). Once present, high humidity and temperatures in the 21 to 25°C range favor amplification of bacteria in or on the seed during germination and sprouting (19).…”

Colonization of Arabidopsis thaliana with Salmonella enterica and Enterohemorrhagic Escherichia coli O157:H7 and Competition by Enterobacter asburiae

“…Efforts are under way in several laboratories to understand the molecular mechanisms of survival and growth of human pathogens on plants from the bacterial perspective (7,15,31,48,54,61). However, the plant biology involved in the interaction with human pathogens has not been investigated.…”

Flow cytometry for rapid detection of Salmonella spp. in seed sprouts

“…However, no treatment yet developed has been able to completely eliminate Salmonella or other pathogens from seeds [11,15]. The warm, aqueous, nutrient-rich conditions used to sprout the seeds provide an excellent environment for microbial growth [5,6,7,16]. Remarkably, the doubling time for an S. enterica strain growing on germinating alfalfa seeds has been found to approach that observed for the same strain growing in LB broth, a nutritionally rich medium [16].…”

“…have historically been problematic from a food safety perspective, as they have been associated with several multistate and international outbreaks of bacterial disease over the past decade or longer [3,4]. Pathogens involved in these outbreaks have included Salmonella, Escherichia coli O157:H7, Bacillus cereus, and Yersinia enterocolitica [5,6]. The most common pairing has been Salmonella in alfalfa sprouts.…”