Growth of Escherichia Coli O157 H7 During Sprouting of Alfalfa Seeds

Growth of Escherichia coli O157:H7 during sprouting of alfalfa seeds
Letters in Applied Microbiology
Volume 33 Issue 2 Page 95  – August 2001
D. Stewart, K. Reineke, J. Ulaszek, T. Fu & M. Tortorello

Aims:Escherichia coli O157:H7 was monitored daily during sprouting of alfalfa seeds inoculated at high (3·92 log₁₀ cfu g¹) and low (1·86 log₁₀ cfu g¹) 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 g¹ were reached. Detection limits of two rapid immunoassays, Reveal and VIP, without enrichment were determined to be 5-7 log₁₀ cfu ml¹.

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.