Growth of Escherichia coli O157: H7 and O104: H4 during Sprouting and Microgreen Production from Inoculated Radish Seeds

Introduction:  Sprouts and microgreens are popular tender produce items, typically grown in indoor facilities which allow a higher degree of control compared to open field production. While sprout have frequently been implicated in foodborne illness outbreaks, there is a lack of data pertaining to the microbiological safety of microgreens.

Purpose: The primary objective of this work was to compare the survival and proliferation of Escherichia coli O157: H7 and O104: H4 on radish sprouts and microgreens cultured in a BSL-2 growth chamber simulating commercial sprout and microgreen production conditions. 

Methods: In this study, sprouts and microgreens were produced from radish seeds inoculated with Escherichia coli O157: H7 and O104: H4 and E. coli populations on the harvested products compared using spiral plating and most probable number (MPN) methods with four replicates.

Results: Both E. coli O157:H7 and O104:H4 proliferated rapidly during sprouting, reaching levels of 5.8 to 8.1 log CFU/g and 5.2 to 7.3 log CFU/g, respectively, depending on the initial inoculation levels of the seeds. In comparison, E. coli O157:H7 and O104:H4 populations on harvested microgreens ranged from 0.8 to 4.5 log CFU/g and from 0.6 to 4.0 log CFU/g, respectively. Although proliferation of E. coli O157:H7 and O104:H4 could occur during both sprouting and microgreen growth, harvested microgreens carried significantly less (P < 0.001) E. coli than sprouts produced from radish seeds contaminated at corresponding levels.

Significance: This study provided the scientific data comparing and contrasting the food safety risks of sprouts and microgreens. It underlined the importance of maintaining the microbiological quality of seeds, especially those used for sprouting.