Growth of Escherichia coli O157:H7 during sprouting of alfalfa seeds


Tortorello U.S. Food and Drug Administration, National Center for Food Safety and Technology, 6502 South Archer Road, Summit-Argo, IL 60501, USA (e-mail:


Aims:Escherichia coli O157:H7 was monitored daily during sprouting of alfalfa seeds inoculated at high (3·92 log10 cfu g–1) and low (1·86 log10 cfu g–1) levels to assess the extent of pathogen growth during production.

Methods and Results: Sprouts and rinse water were tested by direct and membrane filter plating on modified sorbitol MacConkey agar and BCM O157:H7(+) agar; the antibody-direct epifluorescent filter technique; and rapid immunoassays. The pathogen reached maximum populations after one and two days of sprouting seeds inoculated at high and low levels, respectively; in either case, populations of 5–6 log10 cfu g–1 were reached. Detection limits of two rapid immunoassays, Reveal and VIP, without enrichment were determined to be 5–7 log10 cfu ml–1.

Conclusions: These results show the ability of E. coli O157:H7 to grow to high levels during sprouting; however, because these levels may be below detection limits, it is necessary to include enrichment when monitoring sprout production for E. coli O157:H7 by the rapid test kits.

Significance and Impact of the Study: The data indicate that sprouts may harbor high levels of pathogens. The appropriate use of rapid test methods for pathogen monitoring during sprouting is indicated.