Growth of Salmonella During Sprouting of Naturally Contaminated Alfalfa Seeds As Affected by Sprouting Conditions

Growth of Salmonella During Sprouting of Naturally Contaminated Alfalfa Seeds as Affected by Sprouting Conditions
2004 FDA Science Forum Poster Abstract: C-31
April 2, 2004
T. Fu1 , O. M. VanPelt2 , K. F. Reineke1 , 1CFSAN/NCFST, FDA, Summit-Argo, IL, 2NCFST, Illinois Institute of Technology, Summit-Argo, IL

Alfalfa sprouts contaminated withSalmonella have been linked to a number of foodborne disease outbreaks in recent years. The source of contamination is frequently the seeds used for sprouting. Many studies have examined the growth of Salmonella during sprouting of contaminated seeds and shown that the pathogen proliferates rapidly and reaches high numbers during sprouting. Most of these growth studies, however, were conducted using lab-scale sprouting systems under conditions very different from those used in commercial operations. Whether similar growth kinetics will be observed during commercial sprouting operations remains to be determined. We have built a mini-drum sprouter equipped with an automatic irrigation system similar to those used in commercial operations. The growth ofSalmonella during sprouting of naturally contaminated alfalfa seeds in this mini-drum sprouter was compared with growth observed during sprouting in jars under conditions commonly used for home sprouting. The level of Salmonella, while increased by as much as 4 logs after 48 h of sprouting in jars, remained constant during the entire sprouting period in the mini-drum sprouter. The effect of sprouting temperature and irrigation frequency on Salmonella growth was examined. Decreasing the irrigation frequency from every 20 min to every 2 h resulted in an approx. 2-log increase in Salmonella counts, and increasing the sprouting temperature from 20°C to 30°C increased the Salmonella counts by as much as 3 logs. Finally, the effect of chemical treatment of seeds on Salmonella growth was examined. Salmonella grew to a slightly higher level during sprouting of seeds treated with 20,000 ppm calcium hypochlorite compared to levels observed with un-treated seeds.

Note from the SproutNet:  Increasing watering frequency to decrease bacterial loads is something ISS discovered several years ago.  OurRota-Tech Rotary Drums are designed to allow for an optimum crop by watering every two minutes.  Bacteria loads, including plant pathogens, decrease in direct proportion to the frequency of watering.  The above research confirms this regarding human pathogens as well.  This is also important because the FDA is looking for methods that provide a 5 log reduction in salmonella and E.coli 0157:H7.  I hope the FDA will consider this simple approach as meeting part of their requirement regarding salmonella.

I also would like to encourage TJ and the folks at the National Center for Food Safety and Technology to continue down this avenue.  We cannot do testing with contaminated seed, but I suspect if they do this test with seed contaminated with E.coli 0157:H7, they will have similar results.  I also suspect that if they increase the frequency of watering even further, they will find further reductions. 

Nice work folks! 

PS A 2-log increase is 100 times as much salmonella.  A 2-log reduction is a 99% reduction.