Fate of enteric pathogens in different spinach cultivars cultivated in growth chamber and field systems

Abstract

Interactions between enteric pathogens and plant hosts have been shown to be multifaceted. This series of studies sought to expand our knowledge in this area and evaluate whether spinach cultivar selection may be used to curtail pathogen contamination and ultimately reduce microbiological risk associated with this crop. As a component to that assessment, potential antimicrobials that were constituents within spinach leaves were first analysed and found to be spatially non-uniform, being more concentrated on the outer edges of the leaves than in the centre of the leaves. Consequently, the entire foliage of a plant was sampled in subsequent studies examining the fate of Salmonella and Escherichia coli O157:H7 on seven cultivars of spinach. Cultivar did not affect the degree of Salmonella internalized into spinach tissue (P > 0.05); however, it appeared that those Salmonella that were internalized were transient residents as the percentage of plants containing this internalized pathogen dropped within 24 h. No relationship existed between antimicrobial levels (total phenols or antioxidant capacity) of the spinach cultivars and the prevalence of plants exhibiting Salmonella internalization or the persistence of Salmonella or E. coli O157:H7 after the plants had been sprayed with the pathogen. In both growth chamber and field studies, Salmonella was more resistant than E. coli O157:H7 to inactivation. Cultivar affected the persistence of both E. coli O157:H7 and Salmonella but the ranking for each pathogen's survival on three of those cultivars differed suggesting the difficulty in finding one cultivar that would be inhospitable to multiple pathogens.