Differences in internalization and growth of <i> <scp>E</scp> scherichia coli </i> O157:H7 within the apoplast of edible plants, spinach and lettuce, compared with the model species <i> <scp>N</scp> icotiana benthamiana </i>

Abstract

Summary Internalization of food‐borne bacteria into edible parts of fresh produce plants represents a serious health risk. Therefore, internalization of verocytotoxigenic E. coli O157:H7 isolate Sakai was assessed in two species associated with outbreaks, spinach ( Spinacia oleracea ) and lettuce ( Lactuca sativa ) and compared to the model species Nicotiana benthamiana . Internalization occurred in the leaves and roots of spinach and lettuce throughout a 10 day time‐course. The plant species, tissue type and inoculum dose all impacted the outcome. A combination of low inoculum dose (~10 2 CFU ) together with light microscopy imaging highlighted marked differences in the fate of endophytic E. coli O157:H7 Sakai. In the fresh produce species, bacterial growth was restricted but viable cells persisted over 20 days, whereas there was &gt; 400‐fold (~2.5 Log 10 ) increase in growth in N. benthamiana . Colony formation occurred adjacent to epidermal cells and mesophyll cells or close to vascular bundles of N. benthamiana and contained components of a biofilm matrix, including curli expression and elicitation, extracellular DNA and a limited presence of cellulose. Together the data show that internalization is a relevant issue in crop production and that crop species and tissue need to be considered as food safety risk parameters.