TY - JOUR
T1 - Quantification and colonisation dynamics of Escherichia coli O157:H7 inoculation of microgreens species and plant growth substrates
AU - Wright, Kathryn M.
AU - Holden, Nicola J.
N1 - This work was funded by the Scottish Government's (project numbers RD2.3.3, RD3.1.3) Rural and Environment Science and Analytical Services (RESAS) Division strategic programme (Food Safety) and the Food Standards Agency (grant FS101056).
PY - 2018/5/20
Y1 - 2018/5/20
N2 - Microgreens are edible plants used in food preparation for their appealing flavours and colours. They are grown beyond the point of harvest of sprouted seeds, and normally include the cotyledons and first true leaves. Their method of production is similar to sprouted seeds, which is known to be favourable for growth of microbial pathogens, although there is little data on the potential of food-borne pathogens such as Shigatoxigenic Escherichia coli (STEC) to colonise these plants. We found colonisation of nine different species of microgreen plants by STEC (isolate Sakai, stx-), with high levels of growth over five days, of approximately 5 orders of magnitude, for plants propagated at 21 °C. STEC (Sakai) formed extensive colonies on external tissue, with some evidence for internalisation via stomatal pores. Several factors impacted the level of colonisation: (1) plant tissue type such that for broccoli microgreens, the highest levels of STEC (Sakai) occurred on cotyledons compared to the true leaf and hypocotyl; (2) the route of contamination such that higher levels occurred with contaminated irrigation water compared to direct seed contamination; (3) inoculation dose, although only at low levels of inoculation (3 log10) compared to medium (5 log10) or high (7 log10) levels; (4) environmental factors, including to some extent humidity, but also plant growth substrate types. It was also evident that a starvation response was induced in STEC (Sakai) in low-nutrient plant irrigation medium. Together these data show that microgreens represent a potential hazard of contamination by food-borne pathogens, and to mitigate the risk, they should be considered in the same manner as sprouted seeds.
AB - Microgreens are edible plants used in food preparation for their appealing flavours and colours. They are grown beyond the point of harvest of sprouted seeds, and normally include the cotyledons and first true leaves. Their method of production is similar to sprouted seeds, which is known to be favourable for growth of microbial pathogens, although there is little data on the potential of food-borne pathogens such as Shigatoxigenic Escherichia coli (STEC) to colonise these plants. We found colonisation of nine different species of microgreen plants by STEC (isolate Sakai, stx-), with high levels of growth over five days, of approximately 5 orders of magnitude, for plants propagated at 21 °C. STEC (Sakai) formed extensive colonies on external tissue, with some evidence for internalisation via stomatal pores. Several factors impacted the level of colonisation: (1) plant tissue type such that for broccoli microgreens, the highest levels of STEC (Sakai) occurred on cotyledons compared to the true leaf and hypocotyl; (2) the route of contamination such that higher levels occurred with contaminated irrigation water compared to direct seed contamination; (3) inoculation dose, although only at low levels of inoculation (3 log10) compared to medium (5 log10) or high (7 log10) levels; (4) environmental factors, including to some extent humidity, but also plant growth substrate types. It was also evident that a starvation response was induced in STEC (Sakai) in low-nutrient plant irrigation medium. Together these data show that microgreens represent a potential hazard of contamination by food-borne pathogens, and to mitigate the risk, they should be considered in the same manner as sprouted seeds.
KW - Journal article
KW - Microleaf
KW - Microherb
KW - Food-borne pathogens
KW - Fresh produce
KW - Food-borne hazard
U2 - 10.1016/j.ijfoodmicro.2018.02.025
DO - 10.1016/j.ijfoodmicro.2018.02.025
M3 - Article
C2 - 29554556
SN - 0168-1605
VL - 273
SP - 1
EP - 10
JO - International Journal of Food Microbiology
JF - International Journal of Food Microbiology
ER -