Internalisation of human pathogens into salad vegetables during germinating and cultivation / Khalilah Abdul Khalil, Keith Warriner and William. M. Waites

Most of the recent food borne outbreaks has linked to Eschericia coli 0157:H7 contamination of salad vegetables including lettuce. Though recent studies have examined the application of E.coli 0157 :H7 and other human pathogens like Listeria monocytogens and Salmonella on mature lettuce, little is known about these attachments of these pathogens to growing plants. The potential of E.coli and L.monocytogens to become internalised into germinating and hydroponically grown lettuce and watercress has been studied. With inoculated lettuce and watercress seeds (107 cfu/g) with E.coli strains and L.monocytogens could be recovered initially from external and internal sites in 4 days old seedling. When 103 cfu/ml of E.coli and L.monocytogens were introduces into nutrient solution of hydroponically cultivated lettuce and watercress, no internalisation of these pathogens was detected. As in the nutrient solution, inoculated pathogens declined significantly (P<0.01) during the initial inoculation period and were undetected thereafter. The current study suggested that the pathogens were able to internalised into germinating lettuce and watercress, however when these pathogens were introduced at low cell densities, pathogens were unable to internalised into inner tissues of salad vegetables. This suggests that the internalisation of pathogens has relied on cell numbers of population.